Different colored MTS?

At the end of summer tubbing last year I found 3 dark brown and black MTS in my tubs. I only had ramshorns, mysteries and bladder snails so far, so I threw them in a new setup. Fast forward to now and those guys have, of course, multiplied like crazy. Anyways not the topic of curiosity, but today I was looking closely into my 125gal(not where MTS were put) and I happened to notice a trumpet snail shell. It was more white or cream colored with very minor patterning. I first figured it was from previous owner of this setup and had always been in the gravel. I, however, started noticing a couple more around the other and upon closer inspection, I noticed these weren't dead. So...now to my curiosity question. Are there different color variants of MTS? Or are they developing this drastic light to dark color difference based on the substrates as they grow? Has anyone else noticed having light cream colored MTS and dark color MTS? If I could figure out how to post pix I would.