How long have you had the frogs? If they're new, they may still be settling into their home. Handling them unduly will also add to stress From what I've heard it's perfectly normal for frogs to take a week or so to settle in, and may not eat during that period.

Are the sides and back of the tank covered in dark (preferably green) material? If not, do so, and it will reduce stress and make them feel more secure.
Also mist, remove poop etc when they are asleep. This way you don't disturb them.

Make sure there's plenty of foliage for them to hide amongst, but from the pictures it looks pretty good.

The redness you see under the skin on the frogs leg is simply muscle! Red leg appears as an angry red on the belly and underside of the legs. As for the dark-to-bright green colour change, you probably don't need to worry about that either. Frogs change colour according to their environment, humidity, temperature and stress.

Good luck