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.