Your newborn will not be able to see more than 6 inches in front of his face for quite some time, and even when he does, he will have no idea what the heck he's looking at. Nursery walls are decorated for parents, not children. You want your son to get acquainted with universe? Invest in some good books and haul them out when he's three. Read to him for 15-30 minutes each night and let him looks at the pictures. In the meantime, paint the walls a soft green.
I'm not so sure on this. I don't entirely disagree with how far a child can see and the concept of the child "not knowing what he's looking at" but some studies have shown an environment a child spend most of its time in can have some impacts on their life in numerous ways. (Granted, other studies suggest otherwise.)
Soft colors, soft shapes should all be pleasing to the eye of both the parents and child. Beyond personal feelings I don't think any gender specific colors/shapes/visuals need be considered and you need not write calculus equations on the walls to "make the kid smart" because they're not going to mean anything to him until he's 20 and probably not even then.
I would think making the place as neutral and "inviting" as possible would be a good route to go.