Remember that boys are very rambucious and it will get dirty easily and have things thrown at the walls if they are still young. The color scheme should be fairly neutral as the boys interest will change often and you can't keep repainting the bedroom everytime. Also chalk board paint might be a good idea for one wall.
If your child is old enough to speak you should ask him what he likes. As what colors and activities he likes to do. If his favorite color is green, pick a green color to go on his walls. Kids love to help their parents design and decorate their bedrooms.