The way I generally go about making a shading layer is by adding a Multiply layer above the layer with the colors, then painting in the shaded areas with the same color. That makes for a darker resulting color underneath. For highlights (I don't use those often, sadly), I just use a Divide layer.

You can see how that works out on my comic. It's how I do things.

The problem is, this doesn't work with all colors. Mathematically, bright colors won't produce much difference, if any at all. Using my comic as an example, Alex's hair (#FFFF00) shows no difference if I use the same color over it on multiply. So that doesn't always work well.

I think I'll swap to a different method next chapter.

Anyhoo, about the pics, I'd say you did a spiffing job. The way you colored things actually added a bit of a textured feel to things (The scroll especially) in a subtle way to make it stand out. Sweet!