The most prominent colour concept in Buddhism is that of the rainbow body, which is the highest level of meditative achievement wherein the body is transformed into pure light. The rainbow body is the highest achievement other than Nirvana, which is the essential end-goal for Buddhists. Since the "pure light" on the spectrum contains all colors, and is white, to possess a rainbow body means to possess all colors, and to do some means meditating on colors that embody specific teachings.
Image from: http://www.rainbowbody.net/images/padmasamrainbow.jpg
