I love that you're challenging yourself to do full illustrations! Colour, light, and shadow all sort of go hand in hand. Hue, saturation, and value are all things you get a feel for from doing studies. It's hard to make suggestions because every piece will have different rules to follow. For an underwater scene, you did a good job of giving things a blueish hue, but I think you forgot to do that for the light coming from above. It was also just really bright. With an underater scenes I like to let light and shadow dictate my forms. So I made everything darker to bring the eye to the focal points and also removed the really saturated areas of red as there were sort of randomly placed and competed with the skeleton and diver for attention. So use reference when you're learning to colour! You'll gradually pick up colour theory as you do. | Artwod Feedback