The underside of my tree frog has a slight redness under it. Since I've had him he has this redness.

Now I understand redness could be a sign of the dreaded red leg; however, whenever I look at other pictures of these frogs I see the gambit run from brilliant white, palish white, to a redness like mine.
I don't see any swelling, he is really active at night (lots of calls and got videos of him hopping or climbing around), he doesn't seem to be losing weight, there is no evidence of bleeding, no cloudy eyes, and crickets are vanishing.

Should I be concerned? I had him for about 4 months so far and the one he came with died to worms about a month after I got them (took him to the vet, isolated them, gave medication to both, we concluded the he was shipped with the disease) so I've been very cagey and watching intently.

Husbandry wise: I never handle him, and I scrub and wash his water dish daily, I used to use de-chlorinated tap water, but I decided to switch over to purified bottle water recently due to concerns with possible irritants. He is also in a bio-reactive terrarium and I take the none living plants and decorations out to scrub monthly. Soil is stirred weekly with adding bio-reactive boosters and food for the spring-tails every week.

I am hoping that it just his natural pigmentation or at worst there are irritants that bothering him.