On color - I'm thinking about it a lot since doing this one. I need those colorful grays! I'm using mostly primaries and secondaries - cartoonish colors. What I need a lot more of is the tertieries - the mixtures of a secondary (orange, green or purple) with its complement (the primary opposite it on the color wheel - for instance red is the complementary of green etc). Tertieries are subtle complex colors that are hard to identify - you can't just instantly say That's a pink, or a yellow, or whatever. So they're the colorful grays - also known as dirtied up colors. They make a painting look more realistic because they're less saturated.
I think one of the reasons I tend not to use them is that you can't get them out of the Photoshop color picker. Unless there's some trick I'm not aware of (there are many!) - all I can get out of it is primaries and secondaries - so I need to grab a complementary to some color that's already on the painting or make a floating palette and mix colors on, and blend them together, then paint with it.
Also I need to use a lot more black and white. In fact, I want to do some exercises by starting with a bold line drawing done in black, with the darkest shadows filled in solid black, and put down a middle value color and then white for the highlights, and paint it up from there. That way I won't be afraid to drop in those full blacks and whites, which is a problem for me. If you don't have them already on the image, your eye fools you into believing you have a good full range of values. Until you compare it side by side with another picture that actually has a full value range, and suddenly you see how woefully inadequate yours is!