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RESEARCH ARTICLE
Inter-rater reliability of vehicle color
perception for forensic intelligence
Khai LeeID
1☯
, Anis Amanina Abdul Fatah
2☯
, Nuryuhanis Mohd Norizan
2☯
, Zakiah Jefrey
2☯
,
Fatin Hanani Md Nawi
3☯
, Wan Fatihah Khairunisa Wan Nor
3☯
, Huan Xin Wong
4☯
, Saiful
Fazamil Mohd Ali
5‡
, Poh Ying Lim
6‡
, Kah Haw ChangID
1‡
, Ahmad Fahmi
Lim AbdullahID
1‡
*
1Forensic Science Program, School of Health Sciences, Health Campus, Universiti Sains Malaysia, Kubang
Kerian, Kelantan, Malaysia, 2Faculty of Resource Science and Technology, Universiti Malaysia Sarawak,
Kota Samarahan, Sarawak, Malaysia, 3School of Marine and Environmental Sciences, Universiti Malaysia
Terengganu, Kuala Terengganu, Terengganu, Malaysia, 4Department of Chemistry, Faculty of Science,
University of Malaya, Kuala Lumpur, Malaysia, 5Criminalistic Section, Forensic Division, Department of
Chemistry, Petaling Jaya, Selangor, Malaysia, 6Department of Community Health, Faculty of Medicine and
Health Sciences, Universiti Putra Malaysia, Serdang, Selangor, Malaysia
☯These authors contributed equally to this work.
‡ These authors also contributed equally to this work.
*fahmilim@usm.my
Abstract
The topcoat color of motor vehicles offers vital information while investigating vehicular acci-
dents, especially in instance of hit-and-run, since witnesses seldom perceive and retain the
plate details. Differences in color perceptions among individuals with normal vision may
lead to confusion in determining the color of the car involved. In this way, witnesses of crash
accidents could potentially initiate flawed leads in forensic investigation, and thus affect the
administration of justice. In this study, the inter-rater reliability of vehicle color determination
by different volunteers was explored. Six individuals observed the topcoat colors of 500 sta-
tionary and 500 moving vehicles from five locations, employing a common system of color
gradation. The outcome was binary: the vehicle color was either a “match” or “non-match”.
This was followed by statistical analysis in terms of the colors’ frequencies and inter-rater
reliability, based on which more suitable color descriptions were determined for subsequent
comparisons of stationary and moving vehicles. Higher match frequencies and greater inter-
rater reliability were observed when color gradations were disregarded. The frequency of
correct matches could have been closely related to their relative on-the-road distribution,
regardless of the statuses of observed vehicles. It was also found that black and white were
associated with a greater number of matches than were intermediate colors, which should
be carefully interpreted during forensic investigation to avoid wrong leads. In conclusion, the
present study demonstrated the forensic significance of vehicle topcoat color determination,
particularly in cases where witness statements are crucial.
PLOS ONE | https://doi.org/10.1371/journal.pone.0218428 June 18, 2019 1 / 10
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OPEN ACCESS
Citation: Lee K, Abdul Fatah AA, Mohd Norizan N,
Jefrey Z, Md Nawi FH, Wan Nor WFK, et al. (2019)
Inter-rater reliability of vehicle color perception for
forensic intelligence. PLoS ONE 14(6): e0218428.
https://doi.org/10.1371/journal.pone.0218428
Editor: Barry Rosenfeld, Fordham University,
UNITED STATES
Received: August 30, 2018
Accepted: June 3, 2019
Published: June 18, 2019
Copyright: ©2019 Lee et al. This is an open access
article distributed under the terms of the Creative
Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in
any medium, provided the original author and
source are credited.
Data Availability Statement: All relevant data are
within the paper.
Funding: This research is funded by Universiti
Sains Malaysia Short Term Grant (304/PPSK/
61313156). Abdullah AFL is the author who
received the funding. The funders had no role in
study design, data collection and analysis, decision
to publish, or preparation of the manuscript.
Competing interests: The authors have declared
that no competing interests exist.
Introduction
Multiple coatings of automotive paints are applied to vehicles for both protective and decora-
tive purposes [1,2]. These paints are frequently encountered as trace evidence in vehicular
accidents, allowing for the association of questioned samples recovered from a scene with con-
trol samples of known sources through forensic examination. In certain vehicular accidents
such as hit-and-run, the investigative team would look for the plate number and color infor-
mation alleged by a witness or victim of the accident in order to begin their investigation.
Unfortunately, in cases where witnesses either did not notice or cannot remember plate num-
bers, the colors of vehicles, the descriptions of which are based solely on the perceptions of wit-
nesses, become the main lead. Therefore, the inability to correctly describe the colors of
vehicles may lead investigations astray.
During a trial, investigative officers or forensic scientists are often required to explain the
evidential value of questioned paint evidence recovered from a vehicular accident, including
its color [3,4]. Surveys and compilations of vehicle color distributions generalized as topcoat
color [5] (technically, unlike the solid paint system, the top layer of a metallic paint system is a
colorless clear coat that covers the metallic basecoat) have been conducted to assess the proba-
tive value of a vehicle’s color in supporting forensic conclusions [3,4,6–11]. In addition, color
determination through careful interpretation of submitted paint samples can also be correlated
with the color momentarily perceived by a witness during an accident, although this is often
difficult. Any lack of accuracy in describing the color perceived by a witness, and especially so
if there are two or more witnesses, would impact credibility during cross-examination [12].
Though a standardized color coding system for paint has been established in the forensic com-
munity [13], it is not readily available to the public, complicating the process of accurate iden-
tification of topcoat color. Previous literature has suggested the possibility of variations in
color perception by individuals with normal vision [14–16], supporting the likelihood of such
differences generating flawed investigative leads or contradictory testimony.
Inter-rater differences in color determination could be related to categorical differences in
observers’ knowledge and perceptions [17]. Color perception is an observer’s ability to percep-
tually differentiate between colors [18], which could be subjectively affected by personal, cul-
tural, and national beliefs, values, prejudices, and other unknown factors [19]. In view of this,
the inter-rater reliability of vehicle topcoat color perception is a topic of interest in forensic
intelligence, and the aim of this study was to evaluate inter-rater differences in descriptions of
vehicle topcoat color in both static and moving conditions. Based on a prevailing system [3],
the topcoat colors of stationary and moving vehicles were surveyed and statistically analyzed.
A better color description system was highlighted to increase the agreement percentage among
observers. The inter-rater reliability of vehicle color determination among observers was eval-
uated and colors that could potentially lead to incorrect determination were also identified. To
the authors’ knowledge, a survey of this type has not been reported thus far. Such information
can serve as an initial lead for investigative teams to verify a witness statement, and subse-
quently assist forensic teams in tracing the vehicle involved in an accident.
Materials and methods
Survey
This study was conducted in five locations within the boundary of the Health Campus of Uni-
versiti Sains Malaysia, where a total of 500 stationary and 500 moving vehicles were randomly
sampled and studied. Topcoat colors of vehicles were observed at noon in clear weather by six
students (aged between 20 and 22 years) from various universities undergoing industrial
Inter-rater reliability of vehicle color perception
PLOS ONE | https://doi.org/10.1371/journal.pone.0218428 June 18, 2019 2 / 10
attachment training in the forensic science program. In this study, only passenger-type vehi-
cles, such as cars and vans, were included; heavy-duty vehicles such as trucks and buses were
excluded.
Prior to the survey, the authors conducted an introductory session with the six observers
using a standard auto color chart available in forensic laboratories as a guide. This was to
assure consistency in color determination, noting the choice of colors available and the color
naming system. Buckle et al.’s [3] chart consisting of 29 grades of colors was utilized; this infor-
mation is depicted in Table 1. Those colors that could not be included in any of the listed col-
ors in Table 1 were counted as “miscellaneous,” as done in our report on vehicle surveys [6].
In each location, the six observers simultaneously noted the topcoat color of each car at a
distance of approximately two meters. For both stationary and moving vehicles, each observer
was given three seconds to write down their observation on a sheet of paper provided. No
attempt was made to identify whether a vehicle’s paint system was solid or metallic since this is
difficult to determine at a glance. As the survey was conducted within the university, the speed
of moving vehicles could not have exceeded 60 km/hr.
The observers’ perceptions were tabulated. Subsequently, the extent of agreement between
individuals’ observation regarding topcoat color was checked and interpreted. Regarding
Table 1. Color chart.
No. Color [3]
1 Black
2 Light blue
3 Medium blue
4 Dark blue
5 Green-blue
6 Light brown
7 Medium brown
8 Dark brown
9 Red-brown
10 Red
11 Red-orange
12 Gold-bronze
13 Light gray
14 Medium gray
15 Dark gray
16 Light green
17 Medium green
18 Dark green
19 Yellow-green
20 Light yellow
21 Medium yellow
22 Dark yellow
23 Maroon
24 Orange
25 Purple
26 Pink
27 White
28 Off-white
29 Miscellaneous
https://doi.org/10.1371/journal.pone.0218428.t001
Inter-rater reliability of vehicle color perception
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agreement, the outcome was binary: it was either a “match” or “non-match.” It was a match
when all the observers described the same color code, while it was a non-match when even one
observer varied in his/her description of the topcoat color.
Statistical analysis
Statistical analysis was conducted using Stata software version 12 (StataCorp, USA). Data
cleaning and descriptive analyses were performed to ensure there were no errors.
Evaluation of agreement percentage in relation to color description
Using the colors listed above [3], the frequency and percentage of matches and non-matches
in observers’ determinations of topcoat colors were calculated. The statistical output using
these colors formed the basic data. Subsequently, shade variations in the colors described in
Table 1 were clubbed together to correspond to the basic color, with matches and non-matches
calculated in this situation as well.
Comparison of inter-rater reliability of color determination between two
different color descriptions
Inter-rater reliability of color determination for both color descriptions was investigated.
Kappa test (κ) statistics were used to assess agreement among the six observers. These values
were interpreted as poor agreement (0.00–0.20), fair agreement (0.21–0.40), moderate agree-
ment (0.41–0.60), good agreement (0.61–0.80), and very good agreement (>0.80) [20]. In this
study, κstatistic values >0.60 were considered indicative of good inter-rater reliability and
<0.60 of poor inter-rater reliability. A p-value <0.05 was considered statistically significant.
Based on the statistical output, a color description with better inter-rater reliability was deter-
mined. The inter-rater reliability of moving vehicles was also verified using the color descrip-
tion determined in the previous section.
Determination of “non-match” color combinations among observers
The observational data set was further analyzed to determine the colors with a greater possibil-
ity of non-matches among the six observers. The frequency and percentage of the matches and
non-matches for each color were demonstrated and compared. Colors that could easily be
described differently by the six observers were identified.
Results
In this study, 214 matches were recorded, which was 72 cases less than the non-matches. This
finding indicates that all six observers concurred in the descriptions of only 42.8% of topcoat
colors when using the color shades described earlier [3]. Then, basic colors alone were used by
totaling the light, medium, and dark colors into one group. For instance, “light gray”‘,
“medium gray,” and “dark gray” were all clubbed together as one basic color: “gray.” When the
variations in the shades were eliminated, there remained 18 colors and the consequent fre-
quencies of matches increased by 153, constituting of a total of 73.4%.
Inter-rater reliability (κ) values for each color scored in the two calculations (one that
included the variations in shades and the other that considered the basic colors) were com-
puted (Table 2). By including the variations in shades as in the prevailing color description [3],
black, orange, pink, purple, and light gray recorded very good agreement (κ>0.80), followed
by maroon, dark green, white, medium blue, red, light brown, light green, light blue, and dark
gray with good agreement (0.61<κ<0.80). These colors demonstrated good inter-reliability
Inter-rater reliability of vehicle color perception
PLOS ONE | https://doi.org/10.1371/journal.pone.0218428 June 18, 2019 4 / 10
(κ>0.60). It was also found that the intermediate colors (i.e. green-blue, yellow-green, red-
orange, gold-bronze, and red-brown), as well as miscellaneous shades of basic colors, exhibited
poor inter-reliability (κ<0.60).
Using basic color descriptions, the number of matches decreased by 12 when vehicles were
in motion (Table 3), but the status of vehicles, either stationary or in motion, did not affect the
correct determination of vehicle topcoat colors under the observational conditions. Among
the six observers, regardless of whether the vehicles were stationary or moving, white, gray and
black were the top three matches and were ranked the same. The high match frequency of the
color blue among stationary vehicles was found to decrease when observing moving vehicles.
Red was the fourth most frequent match for moving cars. Overall, inter-rater reliability for
both stationary and moving vehicles demonstrated very good agreement at κvalues of 0.85
and 0.84, respectively.
Table 2. κvalues of each color in two different color descriptions for stationary vehicles.
Color Inter-reliability (κ) values��
Color chart [3] Basic color descriptions
Black 0.96�0.96�
Blue Light 0.65�0.81�
Medium 0.72�
Dark 0.44
Green-blue 0.56 0.56
Brown Light 0.68�0.65�
Medium 0.15
Dark 0.44
Red-brown 0.22 0.22
Red 0.68�0.68�
Red-orange 0.52 0.52
Gold-bronze 0.32 0.32
Gray Light 0.89�0.91�
Medium 0.45
Dark 0.63�
Green Light 0.67�0.79�
Medium 0.12
Dark 0.77�
Yellow-green 0.52 0.52
Yellow Light 0.31 0.62�
Medium 0.40
Dark 0.23
Maroon 0.78�0.78�
Orange 0.92�0.92�
Purple 0.91�0.91�
Pink 0.92�0.92�
White Pure white 0.73�0.98�
Off-white 0.41
Miscellaneous 0.40 0.40
Overall 0.69�Good agreement 0.85�Very good agreement
�Good inter-rater reliability (κ>0.60)
��Reliability test was significant, p<0.05
https://doi.org/10.1371/journal.pone.0218428.t002
Inter-rater reliability of vehicle color perception
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In this study, a non-match was scored if there was even a single difference among observers.
Therefore, cases involving determination of two or more colors by the six observers were sepa-
rately recorded as non-matches in their respective color categories. White scored the lowest
percentage of non-matches, followed by black and gray. On the contrary, there were colors
with only non-matches, such as red-brown, gold-bronze, and yellow-green, where no agree-
ment was achieved among observers. It was also noted that the colors that could lead to differ-
ences in color determination were similar, regardless of whether the vehicles were stationary
or moving.
Discussion
The majority of non-matches reported in this study were seen as a consequence of the exis-
tence of multiple shades of the same basic color. For example, the six observers did not have
mutual agreement in determining “white” and “off-white” where 81 cases, accounting for
28.3% were recorded as non-matches. “Dark gray” and “medium gray,” with non-matches
recorded in 22 cases (7.7%), and “light gray” and “medium gray,” with non-matches recorded
in 21 cases (7.3%), showed similar trends. The higher proportion of matches reported when
considering only the basic color description as compared to when shades were included [3]
indicates the value of basic colors.
When shade variations in blue, brown, gray, green, yellow, and white were disregarded, the
inter-rater reliability increased considerably. White, which was initially coded separately as
“white” and “off-white,” became the most reliable color, replacing black. In the basic color
description, only the crossover colors (i.e. green-blue, yellow-green, red-orange, gold-bronze,
Table 3. Percentages of match and non-match frequencies based on color description.
Color Stationary vehicles
“Match” (n = 367)
Moving vehicles
“Match” (n = 355)
Frequency (%) Frequency (%)
Match Non-match Match Non-match
Black 56 (81.2)�13 (18.8) 56 (76.7)�17 (23.3)
Blue 26 (44.1)�33 (55.9) 17 (42.5)�23 (57.5)
Green blue 1 (20.0) 4 (80.0) 0 (0) 4 (100.0)��
Brown 8 (18.6)�35 (81.4) 12 (22.2) 42 (77.8)
Red-brown 0 (0) 28 (100.0)�� 0 (0) 15 (100.0)��
Red 7 (19.4) 29 (80.6) 30 (58.8)�21 (41.2)
Red-orange 1 (4.2) 23 (95.8)�� 1 (5.6) 17 (94.4)��
Gold-bronze 0 (0) 14 (100.0)�� 0 (0) 12 (100.0)��
Gray 120 (70.2)�51 (29.8) 82 (59.0)�57 (41.0)
Green 7 (28.0) 18 (72.0) 10 (27.8) 26 (72.2)
Yellow-green 0 (0) 7 (100.0)�� 0 (0) 5 (100.0)��
Yellow 3 (23.1) 10 (76.9) 4 (28.6) 10 (71.4)
Maroon 4 (28.6) 10 (71.4) 1 (20.0) 4 (80.0)
Orange 2 (66.7) 1 (33.3) 3 (37.5) 5 (62.5)
Purple 7 (58.3) 5 (41.7) 11 (91.7) 1 (8.3)
Pink 3 (60.0) 2 (40.0) 1 (33.3) 2 (66.7)
White 122 (92.4)�10 (7.6) 121 (92.4)�10 (7.6)
Miscellaneous 0 (0) 3 (100.0)�� 6 (26.1) 19 (73.9)
�top five “match” scores
�� top five “non-match” percentages
https://doi.org/10.1371/journal.pone.0218428.t003
Inter-rater reliability of vehicle color perception
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and red-brown) demonstrated poor inter-reliability (κ<0.60), suggesting differences in agree-
ment on such intermediary shades of colors.
Although an introductory session was conducted to calibrate the observers prior to sam-
pling, the variations in color determination could have been due to differences in their ability
to discriminate colors as well as personal experiences [19,21]. A significant increase in the
overall inter-reliability from 0.69 to 0.85 was observed when shades were discarded, resulting
in very good agreement. Higher reliability in single-color determination was also achieved by
disregarding the shade variations in basic colors. This observation was in agreement with Bae
et al. [22], who found that colors were easier described by a single term (e.g. gray) rather than
including shades (e.g. light gray, medium gray, or dark gray) since the boundaries between
these shades differ among individuals. The suggestion of the possibility of eliminating color-
specific biases by merging shades into one color ensures better appreciation of the categorical
boundaries of basic colors [22]. This was supported by the better scores and reliability obtained
when the different shades of a color were combined.
Since all six individuals in this study made their observations in similar conditions, the use
of only basic colors, which ensures good inter-rater reliability, is proposed for describing vehi-
cle topcoat colors during forensic investigations, particularly when recording witness state-
ments. In addition, such basic color-based enquiries would limit the use of jargon, thus
conforming to the suggestion that an observer feels more comfortable describing a color in a
few words rather than having to rely on a spectrum of colors with broad and hardly discrimi-
nable shades [23]. However, it is also important to note that the investigative team should
gather as much information as possible from a witness as he/she is able to provide.
Higher match frequencies for white, gray, and black could be linked to the on-the-road top-
coat color distribution found in an earlier survey [6]. A greater number of vehicles top-coated
with these colors could have been observed during the present survey, accounting for approxi-
mately 80% of the total matches. However, it has to be emphasized that the on-the-road distri-
bution of topcoat colors could not be linked to the inter-rater reliability in color determination
since certain colors such as pink, orange, and purple that have been reported to have very
good inter-rater reliability were not among the common topcoat colors of vehicles in the coun-
try [6]. The rarity of a color does not appear to influence inter-rater reliability of color
perception.
Good inter-rater reliability indicates greater consistency in the estimation of a phenome-
non; in this case, matches during color determination. The use of basic colors has been associ-
ated with more consistent determination and less confusion as compared to the use of
intermediate colors [24]. In this study too, basic colors like white and black had high inter-
rater reliability values of 0.98 and 0.96, respectively, during matches. Contrarily, in the case of
colors like green-blue, yellow-blue, red-orange, gold-bronze, and red-brown, poor inter-rater
reliability values were attributable to a large percentage of non-matches based on the criterion
that disagreement by even a single observer was categorized as a non-match (Table 3). The
identification of intermediate colors, such as the combination of red/red-brown, red/red-
orange, brown/gold-bronze, and red/red-orange/red-brown, was likely to be incorrect. How-
ever, it is important to be aware of the possibility of wrong matches even if a particular color
demonstrated good agreement regarding inter-rater reliability value. For example, the deter-
mination of the color gray was associated with a relatively large percentage of non-matches
(29.8%), wherein gray could be confused with blue, brown, or even white.
This study suggests that witness statements regarding intermediate colors should be care-
fully interpreted during forensic investigations to avoid following wrong leads. Additionally,
exact agreement among the observers which did not occur, particularly in determination of
intermediate color, could have been due to personal variations [18,19]. This is exemplified by
Inter-rater reliability of vehicle color perception
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the non-matches for white (Table 3), which appears unique and the least confusing. While it is
highly likely that such a color will be correctly determined by a witness, it is not certain because
of differences in individual perception [17,18,22]. In fact, the outcome of this study could aid
in investigative procedures where a search for a vehicle of a specific color can be broadened to
other possibilities whenever a witness can provide more detailed color information.
According to Bae et al. [22], an observer’s visual system can spontaneously assign category
labels to signals that interact with encoded shade content to produce bias during response, par-
ticularly when an observer is required to describe the vehicle topcoat color after having seen it
just once. In other words, observations regarding moving vehicles could lead to delays in
encoding colors, which is unlikely to happen for stationary vehicles; the consequently greater
bias could be the cause for the slightly lower inter-reliability values among moving vehicles
[22]. In this study, although the observational results demonstrated a slight decrease in the
overall inter-rater reliability for moving vehicles, a significant association between the matches
in color determination was lacking for both stationary and moving vehicles.
Previous literature suggests that memory retrieval delays could affect observers’ color per-
ception [25,26], especially because of distractors such as surface illumination and the motion
of an object [27,28]. In this study, possible distortions or biases caused by delayed memory
were minimized through the provision of sufficient time to assign a color to the moving vehi-
cles, leading to no significant effect on observers’ color perception. Short-term memory could
be one factor leading to variations in color determination [28,29]; nonetheless, future studies
on its relationship with color perception, which could offer useful retrievable information to
law enforcement authorities, are recommended.
This study was conducted in optimal rating conditions with adequate illumination at a
fixed distance for the young observers to determine topcoat colors. However, further collation
of information, including vehicle color perception under different conditions, particularly
accounting for environmental factors and observers’ vision and attention toward color deter-
mination, is necessary for broader forensic intelligence. However, percentage of agreement
among colors with greater number of observers observing on the smaller number of objects
could be proposed, perhaps in subsequent studies upon the determination of suitable color sys-
tem and combination of “non-match” colors identified in the current study.
In general, the frequency of matches in topcoat color determination, both for stationary
and moving vehicles, could be related to their relative on-the-road distribution. This study
indicated that using basic colors without shade variations could lead to better determination of
color by an observer, resulting in a greater frequency of matches. The motion of vehicles did
not have much effect on the scoring a match, given that the environmental conditions were
adequate for an observer to encode the color. This study supports that for forensic intelligence
purposes, cases involving descriptions of vehicle topcoat colors shall need greater investigative
efforts including a more careful interpretation of witness testimony. It should also be empha-
sized that individual differences could lead to differences in color perception, especially when
involving intermediate colors.
Conclusion
A survey to investigate the inter-rater reliability of color determination among observers who
visually perceived the topcoat colors of both stationary and moving vehicles indicated that the
frequencies of matches, and subsequently inter-rater reliability of color determination among
observers, significantly increased when using basic color descriptions, disregarding their
shades. White and black had the greatest matches, while intermediate colors like green-blue,
yellow-green, red-orange, gold-bronze, and red-brown were considered confusing, and thus
Inter-rater reliability of vehicle color perception
PLOS ONE | https://doi.org/10.1371/journal.pone.0218428 June 18, 2019 8 / 10
require careful interpretation during forensic investigation. Information from this study can
prove useful in interpreting witness descriptions of vehicle topcoat colors for more reliable
statements.
Acknowledgments
Special thanks to Associate Professor PT Jayaprakash and Associate Professor Lim Boon Huat
for editorial assistance.
Author Contributions
Data curation: Khai Lee, Saiful Fazamil Mohd Ali.
Formal analysis: Poh Ying Lim, Kah Haw Chang, Ahmad Fahmi Lim Abdullah.
Investigation: Anis Amanina Abdul Fatah, Nuryuhanis Mohd Norizan, Zakiah Jefrey, Fatin
Hanani Md Nawi, Wan Fatihah Khairunisa Wan Nor, Huan Xin Wong.
Methodology: Kah Haw Chang, Ahmad Fahmi Lim Abdullah.
Supervision: Ahmad Fahmi Lim Abdullah.
Validation: Poh Ying Lim, Kah Haw Chang, Ahmad Fahmi Lim Abdullah.
Writing – original draft: Khai Lee.
Writing – review & editing: Saiful Fazamil Mohd Ali, Poh Ying Lim, Kah Haw Chang,
Ahmad Fahmi Lim Abdullah.
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Inter-rater reliability of vehicle color perception
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