A drug carried in McCoy's medical kit, Melanex causes brief unconsciousness and temporary skin discoloration. In 2269 (stardate 5591.2), 10 cc's of it is used on Spock, to fake an injury so that a rescue party on the "shore leave" amusement park planet can gain access to the underground bunkers where the Master Computer is housed. It does not change Spock's skin color.