"Emerald' Crab..?

OK, So my tank has survived for over a year. Good times and bad have come and gone. I still love the hobby and my tank. So much, I bought a 30G to start another set up in my office.
I just re-stocked my crabs and shrim. I traded a mean Tang for store credit after he shredded my Banded Coral Shrimp.
Anyway... my question is this...

I thought all of my original stock of crabs were gone, but happened to come across one this morning that survided. When I bought it, I was told it was an Emerald Crab.. "weird" I thought, since it was red (looked identicle to the Emerald except color). I really didnt care anyway.
His color has gone from red to a pink so faint he is nearly white... and butt ugly!
What would cause the color change on such a drastic level?

 

IMO food and water conditions. (lack of food) and bad conditions

I used to have some as well, and when their food source depleted I noticed alot of them change colors to a whiter color. Then they died shortly after.

 

I'm going to guess that it's getting ready to molt

 

Could be that also, I guess I wan't thinking

 

i forgot where i saw it, but there's a website on here selling red "emerald" crabs... methinks it may be reefermadness.us but as far as the color change, i'm stumped