Its based on an RGB palette I think. 256 being he highest value you can set which makes a difference.
I think the way it works is
Red Green Blue ??
[]={0.000000,0.000000,1.200000,2.400000};
By mixing values of the various types. You can create other funky colors (pink tracers anyone?). It might not be in that particular order {R,G,B,?}. It may however. Fiddle around with them and see what you come up with.