That is one nice specimen.. It looks as if it's a Crocea at first because of the shell, it seems almost flat ( characteristics of a Crocea) but then again you can see little scales which is a characteristic of a Maxima... But a dead giveaway to me is the mantle extension.. It definetly looks like a Gold Maxima to me... Gold maxima's are usually brownish ( goldish;) ) with green and little hints of blue at times, and even black and some white!

It's definetly a Maxima, there is no Gold Crocea so there is the biggest giveaway... Nice specimen! What size is it?

How common is it for them to turn color, say green.

I'm guessing you didn't know it was a Gold Maxima, so you asked why it was green.. I answered it..:)

Well that explains the green, he mustve lost his color in the store a little. Heres a shot of him now. Hes about 2.5 inches.