I forget if GIMP works the same (I use Photoshop, and haven't used GIMP in like 5-6 years lol). You should try drawing paths based on what you want to color specifically for ex. Noel's gloves and the like. Also, use the color palette for reference or if it has something similar to the eyedropper tool use that it helps a lot!
I'll recolor it since you want to work on stick art (Don't want you to be stuck forever lol), but you can still try your own!