Once in a while, I'll do a color guide for a specific page. Generally speaking, it's only when I'm married to some specific lighting or have an idea in my head that I can't shake loose. In this case, I wanted the shadow modeling to convey more of the tension in Scott's expression. I also wanted that cast shadow from his hand in there. All of it adds to the drama.
Lighting, to me, is a very important aspect of any drawing. Even when it's simply a black and white illustration. When you have the opportunity to work with color - take full advantage of it and use tone/value/hue to help tell your visual story.
Of course, it's entirely up to the colorist to use my notes or discard them. He may have an even better idea for this page... We shall see!