You thought you'd get to color now, but no! There's still more to do. We're going to make a special layer that when you color on it, it only colors the white parts and leaves the black line art black. It sounds like magic but it's actually a pretty common technique so don't go get packed for Hogwart's just yet. I've brought in the Chief for this job, since I know you've all been missing him, and because Cortana is about ten times harder to color than he is.
This is pretty straight forward. Just select the character, create a new layer, and fill that layer with a color. Doesn't really matter what color.