The obvious answer is that they are very different. In a colloid, there is no requirement that the dispersed gold be in the form of isolated atoms. Colloidal gold is in the form of nanoparticles, each having many atoms of gold (see https://en.wikipedia.org/wiki/Colloidal_gold).
Note that gold is naturally monoatomic, and does not bind to itself chemically, unlike oxygen, which binds in pairs to achieve energetic stability.
With the application of ultrasonic energy a colloidal gold may be easily prepared with a particle diameter of less than 10 nm and suitable for use as an immunological marker for TEM-studies. This new approach replaces the use of phosphorus, traditionally used for producing gold sols of the smallest diameter.