The Colors of Space (annotated)

Bart Steele has just graduated from the Academy, qualified as an Astrogator. Instead of getting a berth on a human ship, however, he disguises himself as an alien Lhari and signs on to one of their ships, risking his life to break the Lhari's monopoly on intergalactic travel by finding out what element is missing from human attempts to copy the Lhari's star drive.

* Introduction by Ann Sharp, Trustee of the Marion Zimmer Bradley Literary Works Trust.