The “green girl” was the creation of Fred Phillips who also made Spock’s Vulcan look for the original Star Trek television series. Stephen E. Whitfield and Gene Roddenberry recalled in The Making of Star Trek (1968) how Phillips grew increasingly frustrated as three consecutive makeup screen tests, in which Roddenberry’s future wife Majel Barrett had been painted green, came back negative. "Now, Fred Phillips is an exceptionally fine makeup artist and recognized as a top pro in the business. He did a thorough job with the makeup and was quite satisfied with the results. Imagine everyone’s surprise, upon viewing the developed film the next day, to find the actress’ face just as normally pink skinned as ever! There was no trace of green." Gene’s orders to Fred Phillips: “Paint her greener!” The following day the test film again showed her as pink skinned as ever. Even Fred was dumbfounded. Recalling the incident, he says, “We did this three days in a row. We had her so green you couldn’t believe it and she kept coming back pink! Finally we figured out what was happening. The technician over at the film lab would receive the film every day and run it through the development solution. As the image formed on the film, he kept saying to himself, ‘My God, this woman is green!’ And so he kept correcting the film developing process in order to turn her back to normal skin color again!”
Bonus: Below, a rare photo of Shatner and Whitney, made after the second pilot, but before the first filmed episode. The uniform worn by Shatner was only ever seen in these promo photos and never in an episode.
"See, you adjust this satellite dish and you can get hundreds of channels for only dollars a day!"
Bonus: A cartoon from the fanzine "Enterprise Incidents" that echoes the MAD Magazine depiction on a similar occurrence, referenced below it.