Every year we get a few calls regarding maple leaves that have red, green, or black bumps on the foliage. The small raised bumps caused by a tiny mite that feeds on the underside of the leaf causing this tiny Gall to form on the top of the leaf surface. They are most commonly seen on Silver Maple, Red Maple, and sometimes the hybrids like Autumn Blaze Maples.  Although it is a bit strange looking tiny galls do not really harm or affect the tree in any way. No treatment is really necessary, and the leaves are still making food which is their job, so really no cause for concern.