Why is the tan star fishes legs greenish grayish?

My friend just got a new cleaning sand star fish. Its normal color is tan but half of one of its legs are greenish grayish.Do you know why this is happining?Why is the tan star fishes legs greenish grayish?He could simply have gotten the leg injured. I may or may not be an infection (highly unlikely) Even if he looses it he will regenerate. If he is eating and you are target feeding it would be hard to say what happened. Do you have any anemone in the tank?

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