It really depends on how old your son is, and what he is like as a person. Personally I think blue is a bad colour for any room - it is very cold and unforgiving and tends to dominate. Why don't you ask your son what colour he would like? After all it is his room. He will probably choose a colour you hate, like orange, but you can always paint one wall in the colour he likes and do the rest in a neutral shade, or one of those shades which is white with a hint of colour - then if he chose orange, you could paint the other walls in a white with a hint of apricot or peach, and it would all coordinate well. If he's not old enough to speak yet, well, you can paint it any colour you like! Yellow encourages happiness, red aggressiveness.
Depending on how old your son is, blue is the obvious choice for younger boys. Another idea however, again depending on age, is to paint designs or a mural. I found this website here which has some great ideas on designs and murals. It could be an alternative that could provide some more fun and inspiration!
Blue is the main colour but go for something different like orange or green its up to you before he gets to old but you want to go for something bright that makes you feel happy when your in it but don't go to mad you want it to last a while. :)
PINK PINK PINK PINK PINK PINK PINK!!!! And no this will not make him gay =)