Changing from mostly green to mostly brown/tan is normal. An infection will usually be reddish and often swollen as well. You should post a picture of the frog regardless, since pictures are always great
How old/large is the frog? Your temps aren't exactly off, but it may be enough to stress a small one. Generally 80-83 day and 75-80 night is good for little ones (for some reasons babies sometimes react poorly to the higher range of temps that are fine for adults).
You need to figure out a way to keep the humidity more constant; covering half the terrarium lid with clingwrap usually works. It should never get below 75% and 90% is a bit high. They don't like fluctuations very much, so that may be stressing him.
You should answer the questions in the Trouble in the Enclosure sticky. You already covered some of them, but may as well fill out the complete version
http://www.frogforum.net/pacman-frog...enclosure.html