So, if I am painting with watercolors (or oils), and I want to see and experiment how different color combinations would look like, how do I do that. Can I change the colors used in each of the layers? Or once I use a color, I am stuck with it?
I know this isn't exactly what you're looking for but, you can try to creat a layer at the top of the one you want to change colors, than fill it with the color you want to test and try to change it's blend mode.
So, say I paint a sun in yellow watercolor, dry the watercolor, then choose ‘paint inside’ (a slide button in the menu). Then with the watercolor brush (any brush really) I can pick another shade of yellow and incorporate to parts of the sun without going over any color lines and keeping the exact shape a water flow as before. Or I can choose green and turn the whole sun to green just by applying the brush roughly to the whole surface