I have this headcanon now that Boimler met his purple universe self once, and that’s why he started dying his hair.
Wait a minute now, is he actively dying his beard as it grows in? That’s pretty weird, isn’t it? Did he lie in his own personal log about dying his hair, or does the hair dying occur at a follicular level?
That would seem to be a pretty big leap out of character for Mariner. She only acts like she doesn’t have boundaries, but she actually sets pretty rigid limits on where she’s willing to go with people she considers close friends.