I love this question because it is so cool what Fitzgerald did when using the color, yellow, to symbolize the difference between old money and new money in the story. If you look at the things described as “yellow,” they include Gatsby’s car, the eyeglasses of T. J. Eckleburg, girls in yellow dresses at the party, and Myrtle’s yellow brick house. However, Daisy is described as the “golden girl”; the skin on Jordan’s arms is also golden in color. Throughout the novel, Fitzgerald plays with these two shades of yellow. The characters with “old money” like Daisy, Tom, and Jordan have gold descriptions attached to their worth and standing. They are above Gatsby’s “new money” that doesn’t shine as brightly. The color yellow shows that Gatsby will never fit into the high society in which Daisy lives.
Gold is a symbol of wealth and privilege afforded by “real” money passed down through inheritance and “old money.” It depicts a social class that is revered for its prestige and class. Yellow, however, is a dimmer shade of gold; it depicts Gatsby’s attempt to insinuate himself in a class in which he doesn’t belong. He will never make it into this “golden” world of wealth.
According to colormatters.com, yellow can also represent cowardice, deceit, betrayal, egoism, and madness. I think you can see how all of these characteristics fit into the unfortunate story of Gatsby’s futile climb to achieve his American dream.