Pastel wouldn’t cause a yellow stripe to appear along the spine.
I hatched out a clutch from a super mystic x butter pairing, and the butter mystics all have faint yellow striping on them.
Here’s some pictures — don’t worry about the head injuries, they were caused by the snakes trying to escape their tubs. The rack I bought was poorly designed, but the guy who built it replaced it for free with a better built one.
Even my pastel super mojave girl had a faint yellow stripe along her spine, though it seems to have faded with age.
Here she is, one pic with her future boyfriend (my super mystic male… also note her head looks dirty because she somehow got poop on it) and one that shows her head a little better. A pastel super mojave would have a lighter head coloration, like how she looks. Definitely check the head patterns!