This is a fungal disease known as oak leaf blister. It is very prevalent this year due to the cool moist spring. The pale green areas will eventually turn brown as the season progresses. They may drop a bit early this fall.

Infection occurred at bud break. In fact, you'll probably notice that the problem is mostly on the older leaves. Collect and dispose of the leaves this fall. Make sure the tree receives adequate care to keep it vigorous. Vigorous trees are not severely affected.