In the new canon lightsaber color depends on the weilder, the crystal only reflects the character of the wielder.... but what do the colors actually mean...
What I think
Blue = protective
Green = spiritual
Red is tougher but considering count dooku... aggressive and combative don't exactly fit but power hungry/domineering/controlling does.
R plus B = magenta/purple strongly conflicted mace windu fits
R plus G = yellow a color associated with sentinels seems to fit too
What about white = R+G+B? Ahsoka seems like G+B but not R but the crystals were R before she cleansed them.