Kirk bites off a piece of a green food cube in #StarTrekTOS' "The Man Trap" and you can see that it is yellow inside. Based on the sound he makes when chewing on it, I would say it is a piece of apple (maybe very unripe honedew melon) to which green food color was applied.
Follow
@gaghyogi49 - Before Dorothy Duder passed away, I asked her what she used to make the food cubes in In A Mirror Darkly, since they were really close to the TOS food. She recalled that she used food colored melons.
