They change they're colour from time to time, it's nothing to worry about and sometimes it can just be shedding.

Everyone sounds spot on, I would however add a light if you haven't already, something like Zoo Med's Nature Sun or Exo Terra's Natural Light. This provides UVA and keeps them happy, providing a day and night cycle. Some have been kept without but it's best to provide it.

If he/she is just a baby, I wouldn't feed superworms just yet, not until it's a few inches. Crickets and small earthworms are best to start them off with, make sure to gut load them and dust them lightly before feeding. I use Repashy Calcium Plus and use it at every feed as instructed on the tub. When the frogs a little larger then include superworms and pink mice but they're best of as a treat, they're not the most healthiest food items.