A question about American Bullfrog color changes

[AbranV]

I've noticed that my 2yr old female American bullfrog will change color every once in a while.

In her "pretty" phase She will be a deep green grass like color with dark spots.

In her "pale" phase she'll change to a light pastel green with lighter spots.

Sometimes she'll be in her "ugly" phase(wife's words, not mine) very dark green all over almost blending in with the spots, but her lips, shout and eyes, will be a pretty bold green.

Her "under carriage" also changes from a light white /grey color with very dark markings on her legs, to a light cream with light green marking on her legs. Sometimes her patterning on her under side, really stands out, other times you can barely tell its there.

I know some frogs like my PCF's will change with temp. And humidity, but I haven't heard of bullfrogs changing. Has any BF keepers witnessed these color changes with your frogs?

Any thoughts on what can trigger a color change?

Thanks for any help!

[Calubob]

My 6 month old bullfrog is sometimes a light green color and other times a much darker green with a blue tint on his nose. I just assumed it was a temperature thing but I have never been sure.