The tops are fine.
The purple veins may be genetic but that's not always the case. There are issues that can cause purple veins.
What strain is that and have you grown it before to know for sure it's genetics?
Edit. They could use a bit of mag. Use some Cal/mag or Epsom salt.
cal/mag = my cal nit/epsom salt. i'll add about a gram or two more next res change
the strains called purple frosting.
it's a cross between the following
(purple punch x choc frosting)
choc frosting = (norcal do-si-dos x mint choc chip)
i've asked ALOT of questions to a guy that grows this strain recreationally, he's said that purple stems are completely genetics, but now i'm kind of paranoid that you bring it up.
what could be a problem that'd cause purple stems?