Hi,
I haven't been on the FF for a long time, and just peeked in to see what was on with treefrogs...
Nothing really stands out to me as a huge caution. Good your going to cover the sides of the tank, this will help them to feel more secure.
Their color is very dark, the only time I've seen this dark color in my white's, was when he was sick (although he is typically a brownish shade). Are your white's usually such a deep, dark brown?
Have you checked for parasites or protozoa infection? They can tolerate infections for some time, but then one day it can become a real problem and they'll exhibit strange behavior and color.
Your temps could go a little higher during the day (about 82 F) and slightly higher at night (about 75 F), this may help.
Anything else you can think of? Chemicals in house, new pets or children making new and unfamiliar noises? A/C that may be vvented above tank? Anything at all?