/3/ - 3DCG

>>638992
When you're decreasing brightness, you're basically adding black due to the color mode. When you do that, you lose color information, and things tend to ramp up in contrast by a large margin with small edits. When you use colors and shades, you'll have a lot more control over your values. It also looks more artistic. Read up on some color theory, and understand some really basic fundamentals about painting and color mixing. It will help you now, and in the long run, even on things that aren't supposed to look 3d.

As for how to figure those colors out...
You want to use a color picker like pic related.
Notice how the colors on the slider are the compliments of what color you have picked. When you lower the slider, you push it more into the range of the compliment's color, and then you can alter the shade/value with the big square.
I don't know what program that is, but I think Gimp, might have something like that. Photoshop definitely does, you can access it by pressing the "R" button in the color picker.

At the end of the day though, it's your project, so go for what feels best. I'll agree with some of the anons that you're taking quite a bit of time on this, especially the coloring.