The iron parts of Collosus are about 30% of him, the yellow parts of him are like 20% of him and the red is the rest. Yet the yellow gets 6 color slots, and the red and gray get three and four each?
One step further, the red-yellow can be made into a single hue shifted ramp easily. Then the gray would best not be treated as PURE GRAY which is almost never a good idea. You're doing a great job with the reflections on the metal, but grey is dull and almost never occurs in life.
This has a very cool stylization to it, congrats. Clean up and finishing are easy when you get the methods down. But to do proper cleanup first you have to have final colors.