I added a black shirt per a request of another crit (along with some small tweaks. ) The other small shirt\'s color is sand and the background is heather grey. It also works well with silver grey and dark grey.
Let me know your color preference (and of course feel free to post other comments too.)
I think it would look really good on a green background, like the color of the pencil. I'm not sure what you'd do, but i feel like the eye needs a little more to it.
I would say give the brain more realistic textures more fitting of an actual brain, and make the silhouette of the man more akin to that of an actual man.
Let me know your color preference (and of course feel free to post other comments too.)