Trying to determine if your frog has red led is very difficult.
It is believed that red leg is a “stress disease”.
Read over the Red Eyed Treed frog care sheet very carefully to make certain the enclosure is just right for Red Eye Tree Frogs. Correct anything ( if needed) with absolutely as little disturbance the frog as possible. Since he is alone there is no need to quarantine him. Moving him just causes more stress.

The “disease” is really a syndrome, Chase, (a bunch of symptoms). It is confusing because the “redness” on frogs legs does not actually have anything to do with it at all --as many frogs have a natural red hint of color there and would therefore may not be a sigh of illness. For example, One of my red eyes has always had a bit of a orange tinge on his lower belly. If I recall – this orange tinge appeared as the frog matured. The others do not have this all. Another does not have a pure white belly but has a more grayish color. This same frog has very little blue within his side stripes and inner thighs. These colors vary from frog to frog – just like their petty side strips vary.

The “redness” that happens is a result of broken blood vessels leading to a collection of blood under the skin. Therefore in frogs like ours ( Red Eyes) , it can be seen it because of the very light skin color in the belly and inner thigh. Experts are still not sure what (pathogen) causes this. They think that it is dormant in the frog and as opportunistic illness that is related to stress factor that causes a weakness in the frogs immune system.( ie : improper temperature and/or humidity, unclean tank, need water changes or substrate change, too much handling or disturbing the frog, lighting, improper diet, mixing certain species) This is why I suggest checking and reviewing every detail within and around the enclosure –and correct any possible stress factor . If I were suspicious of this in one of my 6 frogs, I would firstly move quickly into a prevention mode. I am not a vet. Unfortunately, as far as I know, there is no cure for “Red Leg”. Just because you see some redness does not mean has it.

Hopefully , other will post to help us understand this better.
Maybe try to get more pis -without disturbing him !

Lynn