I'm in your constructs, mapping your colors.
Here's how to do a particle emitter that goes through 3 colors instead of two:
Have a normal particle emitter. Have it go from black to white or from white to black.
Then apply colormap3 effect and set the 3 colors and position of the middle point.
Can be easily extended to 4 or 5 colors, though I don't know how to make it so you can define the number of colors in the ramp. I'll soon extend to 4 and 5. That'll probably be enough.
Can someone check the shader code and see if I made any horrible mistakes in there? I'm quite new to shader code. Maybe the pixel shader version?
Now, if anyone can imagine a way to have this work with textured particles please do tell.
I can't imagine it without modifying the particle emitter to use a texture as a mask for it's own interpolated color.