I brought a money tree (pachira) home a few weeks ago and since then, a yellowish-greenish discoloration has appeared around the base of the trunks (all but one, as far as I can tell). The leaves still look healthy, aside from the gnaw marks from my cat

google has failed me so far, I only get results about discolored leaves. I really don't think the discoloration was there when I brought it home but I'm not sure how quickly it appeared.

help? I'd like to keep Maude alive :|

So far it looks okay. Sometimes one of the braided stems will die back for unknown reasons while the others remain just fine. That might happen with yours, but certainly hasn't happened yet.

Protect it from too much indoor sun. Water it when the top surface of the soil feels dry. Prune or pinch it back regularly to keep it from getting too tall and leggy.