The default colour transition will be blue to red in a default number of colour bands. I want to be able to specify firstly the number of colour bands and also the colour of the intermediate ones.
Put the bands in a 1D texture. Then use glTexCoord1f instead of glColour to specify the “band index” 0.0 for one end of the bands and 1.0 for the other. This should work. Try it before you say it won’t work on a quad since it’s 2d at least. Then again, you might want something else than what I think you want. If so, you need to explain more.