I don't think that is because i would have thought it would be more red/ oranges but here's some info i found-
"Look at your frog's symptoms. Is it lethargic and unwilling to eat? Is it sitting on the ground rather than the walls or plants? Most importantly, is its stomach tinged with red or orange? If most or all of these criteria are true, then your tree frog most likely has red leg. This disease is generally fatal, unless caught in the early stages. Red Leg Disease is a bacterial infection in amphibians. It is called "Red Leg Disease" because it causes hemorrhages of the leg.
If the sick frog shares a cage with other animals, remove the sick frog IMMEDIATELY as red leg is very contagious.
Create an incredibly clean habitat. Clean a small aquarium, or a very large tupperware (preferably with high sides) and cover with a screen or hole-punched lid. Line the bottom with wet paper towels, and add a small water dish filled with dechlorinated water. You will change the towels and the water every day.
Put the tank in a relatively warm, safe area and cover halfway with a towel, being sure to leave air holes unobstructed.
At this point, wait a day or so to monitor the frog. If it starts to perk up (e.g. climbs the walls and hops around), redness goes away, place one cricket in the cage. If the frog eats it, then you are good to go! Keep the frog in quarantine until it looks completely better (plus one more day), feeding every day.
In the more likely event that your frog is not perking up and/or refuses to eat, you may consider going to a veterinarian (there are many that specialize in exotic pets). They will probably give the frog antibiotics, which may help. Unfortunately, there is an equal if not better chance that they will not do anything, and this treatment is very expensive.
Decide whether to force feed it, or not? Redleg disease often impacts the intestines, so the frog physically cannot handle food (the blood vessels on its underside also burst, causing the red color). On the other hand, if this is not the problem and the frog is simply unwilling to eat, then the frog will grow weak and die if not fed. For most cases I would recommend a force-feeding formula, such as Carnivore Care. This can be mixed with water and fed to the frog with a syringe, with moderate to high success. This decision really depends on your own discretion. A cricket or worm can also be used as force feeding food; simply kill the bug, slide the edge of a credit card (CLEAN!) into the frog's mouth and turn (this should open its mouth), and stuff in the bug.
Watch and wait. As I said above, most illnesses are fatal, but the above steps will ensure your pet's comfort and possibly save its life.
In some early cases red leg can be treated by bathing the frog in a Sulfamethiazine bath (15 ml for every 10 l water) daily for 2 weeks, or a 2% solution of copper sulfate or potassium permanganate for the same period"
The bold part- If this is redleg then maybe some one could tell you whether or not to do that