Thanks to a upload from Vexstacy I will never use grey colors to shade. She posted a tip about useing colors with shading and looking up ''Color theory'' and I did.
you see 4 types of colors combinations in the drawing, all of these combinations will trigger your brain and will feel in harmony with the rest of the drawing. One will have more stimulation then the other. You have more nutral combinations and some more challenging combinations. If you go and google this you will see that nature also plays with these combi's and you will find more info on how to works with them. I hope I will be able to figure out how it will work the best for me!

Just wanted to share this with you guys because it was a real eye opener for me =]

(found this pic on google trough ''color theory shading'')