Nothing, he's probably molting, so don't disturb him!
well in the past mine turned from reddish to lighter
Not internally. They have what is called an exoskeleton. It's a sort of skeleton that covers the outside of the crab on his legs and head. This means that they have to shed this skeleton and regrow a new one as they get older so that they can get bigger.
Typically Hermit crab blood is blue, but at times it can be clear.
It is mainly light brown.
Hermit crabs do not care much for the color of the shell, however, they prefer shells with a pearl lining inside. Ecuadorian hermit crabs are very picky for their shells though! Try to get the same shape and colour of shell for these ones.
The shells can be any color. It depends on what they have available to change into. The crab itself can be a variety of colors, depending on what type they are. Some common hermit crab colors are red, pink, brown, and purple.
Yes, hermit crabs can be red. But more or so often they will be another more common color such as brown.
Not really, they are more of an orange color.
I doubt it.
A sandy tan-pinkish color. The body is usually darker then its shell but not always
they are smaller because the males have to show their dominance!