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.