I knew someone was going to ask that. I was tempted to say a small bit of color is fine in the lights, but what does that mean anyway? Younglion's car WIP is a good example of this

https://srv01.simply3dworld.com/showt...5&pagenumber=3

but since it's hard to quantify, let's just say no color period. There's no denying that greyscale images can be fantastic, so focus on the composition and shape. And value, if you want to go that far. Just try to generate something interesting, abstract or real-life.

If you really don't know where to start, find a creative commons photo and just start blocking out the shapes you see. If you want to be more artsy or something, look up cubism images.