Perhaps, it has everything to do with how many colors would have to be added? I can't imagine a blue skin tone going brown or red, even. I would think a tanned form of the light blue would be a darker blue and perhaps something more like a shade of purple for a burn? As in red + blue = purple? Same for the other colors. A tanned green skin might be a darker green, but what would it look like burnt? An ugly brownish-green? Charred? Red, blue and Yellow are your primary colors. From these three comes all other colors. If you add red to blue you get purple. The shade depends on how much red you add, also how dark the blue is. Same with adding yellow to red gets you orange. If you add yellow to blue you get green. Black and White aren't truly colors. Black is the absence of color whereas white is the combination of all color. Studying light will instruct on that. If, however, you add white to red, you get various shades of pink. If you add red, blue and yellow together you get an interesting shade of brown. If you add black to white you get various shades of gray. Paint can be fun to mix. :) Yes, I took three years of art in school.
Logistically it was probably impossible. Whether or not the modders can figure a way around it, I can't say.
