Are you worrying too much about light? Get the local color in. (Local color = “the color that the object would have in a perfect light”, or 100% light. )
Do you need to separate and color foreground/mid-ground/background? Do you need to separate out any areas of focus and characters?
Do you have a small version of color key on the canvas to sample from? Do you need one, or are you re-creating the colors from memory?