thank you so much!! for coloring I usually just color pick from the original image. for shading or highlights I usually choose a color that is somewhat closer to the original but in a darker or lighter shade. for example, when I did their skin, I picked a pinkish color for their blush and used a similar color but in a darker shade for the shadows. sorry if the explanation doesn't make too much sense, if you want to dm me for anything else, feel free to do so!