Normal for colouring to change?

[Jace]

My American Bullfrog is growing like a weed, and seems to be doing very well. However, I noticed that recent pictures of her show her to be of a lighter colour than pics I had taken a couple of months ago. Do Bullfrogs have drastic colour changes such as this often? Nothing in her environment (temp, humidity etc) is different at all.

First picture is from December; second picture is from yesterday. Oh, and she was tentatively sexed as a female, but I think she is big enough to be confirmed: definitely a girl??? Thanks for the help.