Hey! Good job so far! First thing I'd do is to paint a grey background for better value control. It’s not really advisable to paint on a completely white canvas—or, for that matter, a completely black one (it’s possible, but I’d prefer to avoid it). Keep in mind that each part of the robot is not a flat surface, but it has volume (even if it's just a bit of volume). I added shadows to give it more depth. Since the light is coming from the left, the right side of the robot will be slightly darker. Since the internal parts aren’t fully exposed to the light, you can paint them a little darker as well. Avoid making all the colors too saturated. If the colors affected by the light are saturated, try using desaturated colors in the shadows for better balance. Hope this helps!
