Materials Not Working

I have a model that is unwrapped and textured through UV mapping. In the editor, it looks perfect, but when I render, only half of the model has the selected material, and the other has just a white texture.

How can one model have two different materials? And how would I access this second one? It’s not in the material menu, so I’m guessing it’s just that it has no material applied to it.

Edit: I’m using an imported model, and each of the eyes on the model have two separate materials as well, which are actually in the material list. How were the materials applied to different parts of a single mesh?

Thanks.

Edit:
Nevermind, turns out that it had a bunch of built in vertex groups that I didn’t see. The head group had the wrong texture.