This is a fantastic question. There is much to be said about colors in The Great Gatsby.
First, there is a lot of gold. It is used 14 times in the book. This is to be expected, because if we are talking about the gilded age of wealth, there is nothing more symbolic of this than gold. Gold, from time immemorial, has been the symbol of wealth. So, Gatsby’s parties have gold, food that is dark gold. Jordan’s arms are described as slender and golden. Also Gatsby’s tie is gold. Here is an example:
On buffet tables, garnished with glistening hors- d’oeuvre, spiced baked hams crowded against salads of harlequin designs and pastry pigs and turkeys bewitched to a dark gold.
That said, yellow is also mentioned. Most significantly, Gatsby has a gold limousine. It is an ostentatious party machine. The significance of this is that it is not gold. In other words, it is a very close approximation but not the real thing. It is counterfeit. This shows that no matter how hard Gatsby tries, he will not be accepted into old money.
The other color that is important is green. Gatsby gazes at the single green light on Daisy's dock and this light haunts him. On the one hand, this green light presents a symbol of "go." However, this green light is both close and far away. Nick's reflections really show the elusive character of the color green.
"Gatsby believed in the green light, the orgastic future that year by year recedes before us. It eluded us then, but that's no matter – to-morrow we will run farther, stretch out our arms farther…."
This should get you started.