Emerald Crab?

I got two of them yesterday there only green on mine when you look at them straight on. From the top one is red and the other has a brown/red color.

 

I have a emerald crab that is a light green color and also have on that is a bright pink color....I was told it was a strawberry crab. He only comes out at night...never see him during the day! Cool looking crab tough...

 

That red emerald looks very nice. I gonna go see if I can find one locally. Nickname it a Ruby Crab.

 

Same type of Crab, used to have one myself.... The red ones don't seem to be quite as common, and you can even see light pink ones from time to time...

 

i know reef scavengers sell red mithrax crabs. i would assume thats probably what it is.

 

I had no idea they were red/pink either. I've always had a green one in my tank. Haven't seen him in a few weeks, then the other day I saw a pink one. I didn't put him in there so I have no idea where he came from.
Probably a really stupid question, but they can't change colors can they? Maybe after they molt or something?