I think "adjust the shadows" was what the author meant, but making the characters lighter skinned for appeal would be pretty in-character for the kind of company this is.
The standford experiment has long been considered a hoax, tbc. There's pretty conclusive evidence that Zimbardo explicitly asked/encouraged participants to act in a way that would confirm his pre-established theory. (Edit: oh shit, should've read the full chapter before commenting, lol)
Also...