It depends on many factors, including whether the local gambling commission mandates certain base colors for specific denominations. After that, it depends whether the casino wants colorful chips or not. Certain denominations have certain base colors by law in some states/localities, others don't have mandated colors. Traditionally, the "Vegas" colors are $1: white/blue, $2.50: pink, $5: red, $25: green, $100: black, $500: purple, etc., but that isn't always the case. California colors are different (e.g., yellow $5s, black $20s and white $100s), and Reno colors are all over the place (see my Riversides or the Mapes). But most places, regardless of location, conform to the traditional Vegas colors.
Spot patterns and spot colors are an entirely different matter. These can be almost anything, so long as they aren't identical to another casino's chips, and serve both a functional and aesthetic purpose--the spots help with counting chips in stacks and telling if all the chips in a stack are the same denomination, and the colors are a way to make the chips pretty.