He does appear to be developing the tail sheen. I usually find that males develop the sheen a couple of months after being bought - once they have settled down. Once in good conditions they keep it year-round, but it becomes a lot more vivid in breeding season. Paramesotriton breed either in late autumn or early spring, depending on the species, so I would think that you will have to wait until the next breeding season for any true reeding behaviour.
Chris
