Hey Alessandro, This is a cool character design, nice job. The biggest issue is that all your colors are independent of each other. There is going to be orange reflected in the skin where they are close. The opposite is also true. To lighten a color like green, don't just add white, it makes the color look dead and chalky. You should always add some yellow with it to keep the color alive. That goes for all your colors, you have to color shift when darkening and lightening them. You also need to build more contrast by darkening your shadows and not have them be all the same value. I did a quick paint over to show you what I mean. I hope this helps :)