Well, for one, you're using way too many colors, so you don't have nearly enough contrast. For something that size, you probably don't need more than 5 colors, maybe 6, and hey should all be different. Another issue is that you're using the same hue. The shadows should be something closer to a bluish green, while the highlights should be a little closer to yellow. And actually, being that it's a chameleon, you could actually throw in a bit of brown into the mix - I know that they tend to be a bit stripey.