Synchronous rotation

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Due to synchronous rotation of their moon, the inhabitants of the central body will never be able to see its green side.

In astronomy, synchronous rotation is a planetological term describing a body orbiting another, where the orbiting body takes as long to rotate on its axis as it does to make one orbit; and therefore always keeps the same hemisphere pointed at the body it is orbiting. Another way of describing it is that from the surface of the satellite, the main planet appears to be locked in place in the sky as it slowly rotates.

The Moon is in synchronous rotation about the Earth. In fact, most major moons in the solar system have synchronous rotation due to tidal locking.