Here's another panel from an old issue I colored up for practice. This is from Cable & Deadpool #40.
I'm trying to practice a coloring style that works well on un-inked work, and I think this sketchy type of coloring matches it pretty well. I tighten up the coloring around the focal points (Mystique's face for instance), but allow it to get more impressionistic in other areas (like the background).
It saves time, plus I think it looks pretty cool!