Hmm, how bizarre. Perhaps it was a false alarm. Just checked him this morning, no red legs. Pale, creamy colour just like the rest of the frogs. I'll continue to keep an eye on him though, just to be sure..

*EDIT: I'm feeding all the frogs now, and he doesn't have an appetite.. I'm wondering if he might be having the same problems as my other frog, i.e impaction and tetany resulting from calcium deficiency..