I have been watching the SVS video Digital Illustration Process and really enjoying it but the artist, Shaun Keenan, always finishes with a grayscale painting. He doesn't add color so I don't know if he is intending to only show how to do monochrome illustrations or if he assumes that once you have those grayscale layers, the color is just laid on top. I know that some digital artists do that using multiply layers but when I tried that I found it to be very difficult. I especially found it hard to get the colors the way I wanted them because I had to paint on multiply layers all of the time but I don't know if the problems I had were because I am doing it wrong.
I guess my question is two fold -- do you do grayscale paintings and then place color over them, and if you do, what is your method? And what would be the advantage of doing this over just double checking your values as you paint by putting a desaturation layer over everything?