Can't believe that you do those amazing paintings from little black and white pencil sketches - no color studies? I was looking at another artists blog and he showed multiple color studies for a painting explaining that once he resolves the color study, he can just have fun painting and isn't burdened by having to make color choices while painting.
For me knowing the final values comes first and the color comes second. If you get the values right, the painting usually works. Not that color isn't important, but I do so much wet-in-wet that it wouldn't be possible to follow a specific color study. So I have fun experimenting with color as I follow my values road map during the final painting