Project Burner Damage over Time Icons

I wanted to make the icons for the acid, shock, and fire damage over time effects look a little better than from their original sketch by adding color.

This is my first time using Gimp to digitally color, and I think the results of that are apparent. I tried to use layers of differing opacity to preserve the subtle value which comes from drawing with pencils, but it is tricky, and the acid icon in particular was giving me trouble settling on the right base color. The shock icon has a darker outline, which I think suits it, but all three might benefit from a thicker outline. Finally I played around with the gradient effect on the fire icon for a little while, but I need more practice with the sliders, so that it does not look quite so much like an angry onion. It is a learning experience, and learning is progress. Hopefully these icons will help make the damage over time spinners look a little better and easier to identify than just writing the DoT name in plain text.