Your hermit crab's color is determined mostly by his species, but it can change temporarily when he gets close to molting or more permanently as he matures. If you're worried more about his shell color, buy only replacement shells that you find pleasing.
Molting
Regardless of the type of hermit crab you have, chances are he doesn't look good when he's getting ready to molt. Most hermit crabs turn an ashy gray or beige as they grow. They tend to dig under the sand to finish their molting, so when they emerge, be ready for the fresh, clean look of their natural colors.
Claw Color
The color of your hermit crab's claw can help you decide what species he is. In most hermit crabs, the pincer is the same color as the rest of the body. However, the Caribbean hermit crab has a bluish to purple-colored pincer.
Body and Leg Color
Body and leg color can vary widely between hermit crab species. The Caribbean crab usually has orange or red legs, while the Ecuadorian hermit crab usually stays green or bluish gray on his body and legs. However, his body can change color as he ages to sport a bit more orange or tan, while his legs stay a greenish shade. Long-clawed hermit crabs tend to have tan bodies with a reddish tinge, while the broad-clawed variety can be gray, tan or slightly red.
Shell Color
Choosing shells can be the most enjoyable part of owning a hermit crab. As the crab grows, he needs to change shells. It's best to keep three sizes in your crab habitat so he has a choice when the time comes, with one shell being the same size as his current one—just in case he needs a wardrobe change in between growth spurts. You can buy natural shells in different shapes, picking the colors that you want—pastels, neutral tones or shells with bright speckles. Or you can use the hermit crab to reflect your personality by buying painted shells, or painting some yourself. If you opt to do this, make sure the paint used is nontoxic and waterproof, and paint only the outside, never the inside.
