Hi,

He is really not discolored -- not in a 'bad' way.
They will change color from time to time. Typically........ this is normal
Some may even have little white ( very slightly raised ) bumps on their backs.

So if he is eating and pooping ( without diarrhea) than he's fine.

Read every possible care sheet you can find !

Since the frog's skin helps it to retain moisture - the skin color changes with humidity and temperature in its immediate surroundings.
If the humidity is on the higher side and the temp is lower --- they will be more brown.
If the the temp is higher / and there is less humidity --- they will be more green.

He is like a little combo hygrometer/thermometer

Most important ..........is to maintain the proper temperature. You can always give the enclosure an extra spray if need be.

Be sure you have accurate devices. Use more than one thermometer; move it around.
Most hygrometers are not really very reliable...and should just be used as a guide.