Oaks and Galls

I found this incredibly bright looking growth on an oak leaf in my yard in May and was very curious about what made it turn this color. I suspected aphids, since the underside had this white furry look to it.

One of the leaves had what looked like a mealybug nearby, which feed on plant juices.

I finally got help from our very helpful State Horticulturist, Gary Fish, and his colleagues, who agreed that it was likely to be a kind of gall that is not harmful to the tree. It is similar to Erineum (https://bygl.osu.edu/node/751)