This is something that tends to be given as an assignment, so you could probably find some hints in past CSSM discussions
One of the first things you will need to define is what exactly you mean by "red", "green", and "blue". For example, dark purple has no green and has about half as much blue as red: does that mean that purple should be classified as red? If so, then look at the bottom row of that link and notice that those purples have as much blue as they have red: how do you classify those? Now take one of those and reduce the red setting by one increment: would the color not still be purple and yet the blue would be stronger than the red?
