I would try pushing your highlights further towards white.
Take your lightest blue/green, the color that you have painted his armor, and mix that 50/50 with white. Then pick a place that is easy to fix if you don't like it and just apply the brush carefully to an edge for a nice edge highlight. If it looks good add a little more white to your mix and go to the same edge and do it again but in smaller area. If it keeps looking good go all the way to a small spot of pure white. Then do the same procedure on on the big flat (cylindrical really) parts of his armor but don't go as far as your edge highlights.
Here is a little photoshop example of what I am talking about. It's easier to do the big flat bits with photoshop. Which I think is opposite withe brush.
If it's all good in the 'hood, you could try and darken up your shadows in teh same way but maybe use a really dark brown in.stead of black