Thanks for your nice comment. To be honest, I do have photos that I reference, but it's rather interesting how intuitive things become once it comes down to applying color. It's very tricky to ask one color to represent one area in a vector illustration where there might have had a dozen colors in the same area in the reference photo. That's where the real creativity in creating these images lies - interpreting one, so that it looks like the other, using completely different means.
Yes, you are totally right. That is one of the most important things I have learned. I, like so many of us, started coloring skin with many shades of the same color and it took me a very long time to figure out why it looked so flat and boring. Then I tossed rainbows on the skin and it came to life!