Another artist visiting my Deviantart page -- who usually uses a computer to color -- asked how I handled hand colors. I thought this answer belonged in the creator blog:
"Hm. Well, the obvious answer is practice. I picked out a close range of cool colors and a cool brown. That way it didn't get too noisy.
I don't think much how I do things any more; over 50 years of practice has dumped all the process into the hands and lizard brain.
Negative space is nice -- don't fill up too much, leave some air.
My color sense comes from a lazy brush style. I never used a palette when painting with acrylics -- I mixed on the brush, a bit at a time, and "cleaned" a brush by sprinkling the color across the painting, binding the design together, sometimes just wiping the brush dry on a cloth before tipping the brush in the next tube. I would slightly roll part of the brush in one tube, and part in the next, being careful not to muddy the tube. Then I had a mixed color that wasn't too smooth; there were flashes of both colors suggesting the final impression of color. My own version of pointilism or impressionism, I guess.
I'd choose 3 or four colors for the painting, maybe add some touches of others at the end. A small selection of flat brushes, whose corners I used like chiseled rounds.
It partly came from wanting ease of travel. Three small tubes, a couple brushes, a rag, a canvas -- ready to go.
It ended up forming my color use and eye."