East Egg describes the "white" color of everything, from the white palaces to the white house that Tom and Daisy live in. The Buchanans even wear white clothing, and Tom goes on a tirade about the white race. Gatsby wears a pink suit, which he only changes when meeting with Daisy, where he wears a white suit. Daisy is amazed at all of Gatsby's different color suits, which show how he can wear any color to be in tune with his surroundings.
The valley of ashes is all grey. Myrtle Wilson buys a dog from a gray old man, and even goes inside a taxi with grey upholstery. The Valley of Ashes is dim, hazy, and full of dust.
West Egg is full of many colors: "many-colored glass", to Gatsby's many shirt colors. The color yellow is also important, as Jordan's arm is golden, girls wear yellow dresses, and the music is yellow cocktail music. Even Gatsby's car is golden, which ultimately kills Myrtle. Gatsby's toilet seat is "pure dull gold".
Downtown New York takes its color from the people who are in it. Thus Myrtle gets a grey dog from a grey old man, while Tom pays for her "white cake of apartment". Gatsby on the other hand has yellow and golden colors ascribed to him in Downtown New York.
The green that the Dutch sailors saw, and that Gatsby looked for in the green light on Daisy's dock represents the hopes and longings for the American Dream.