Yellow is bright and aware. We know what it means to be in the pink. Or green with envy. Some of those common meanings are found in The Rainbow Oracle, but the system is also a unique, with meanings that differ from other interpretations of color. All divination works within the parameters of the system being used, whether its casting bones, stones, or shells, picking cards, or rolling color cubes.
Answers tend to be meaningful to the person posing the question.
Again, it's synchronicity. More than twenty years ago, Tony Grosso intuitively developed a way of interpreting color, which guided him in his psychic readings. He asked people to list several colors as quickly as they could think of them. One day Rob MacGregor was looking at Tony's handbook and realized there was one problem with his system. Once you knew the meanings of the colors, the rational side of your mind tended to interfere and help you choose the colors.