HCA: Hermit Crab Association

When I got Maxwell, he was in a magpie shell. Since then, he's worn 2 green turbos. Then after he grew out of the last one, he changed into the smallest dark brown snakeskin/tapestry turbo (this was only a couple of weeks ago). It's the top right shell in this picture:



Since then, he's been hiding under the sand for days at a time, but I've had a couple glimpses. His shell now appears to be a light gray or off-white color! (I'll try to get a pic if I see him tonight).

I'm 100% certain he can't have changed, as
a)all other shells close to his size were temporarily removed from the tank while I was reorganizing the shell shop. The first sighting of the apparent color change was while they were still out of the tank.
b)I have never had a shell in that color at all.

I have also briefly removed him from the tank once in case it was some weird lighting trick, but it still appeared gray. I've rubbed it gently and it doesn't seem to be a buildup of sand, minerals, or anything.

Does anyone have a clue what might be going on?

A fresh polish artificially darkens the colors on a shell. Once it gets worn for a bit - especially if digging or if staying in a moss pit - that polish goes away and the more natural and muted colors show through. If you were to wet the shell it would look intense again. Worn for long enough, and the colored layers will eventually be worn away completely and the white/grey mother of pearl will start to show through.

Huh, that's interesting!

Here's a pic I got: