As requested, a grayscale to color tutorial.
Download for full size.
Yes, there is a lot of text. I hope I explained everything properly. As always, if you have any questions, just ask!
It was brought to my attention that I used a couple of terms that not everyone may be familiar with, so here are some clarifications:
*complementary colors are color that sit directly across from each other on the color wheel such as:
Red and Green
Yellow and Violet
Orange and Blue[link]
Using complementary colors, or colors that are closely adjacent to those colors, creature depth and variety in your shadows and highlights. Try it!
**A good definition of contrast: [link]