You could use just one color of chenille, and just one color of tail material, and unpainted heads, but why would you ?
Three colors can be presented- head, body, tail. If the tail is colored, why not the body ? If the body is colored, why not the head ?
Colors are able to both attract and repel. They are involved with a crappie’s number one sense, his vision. I use colors that are reflective of UV light because I believe the fish utilize low light conditions to their advantage, and UV rules in low light. I use flourescent colors because I believe they are more easily noticed during normal light conditions.
My jigs have three colors - head, body, tail. Certain combinations just seem to work better than others. I paint my heads to try to compliment the others.