Why is the green turtle given this name?

 The green turtle is a sea turtle whose body is highly adapted for swimming.

The green turtle has a wide, smooth carapace, or shell. It inhabits tropical and subtropical coastal waters around the world and has been observed clambering onto land to sunbathe. It gets its name not from its shell, which is olive or brown in colour, but from its greenish skin. It has flippers that resemble paddles, which make it a powerful and graceful swimmer.