its hard to say for sure with the grow light on
but that looks like a micro nute def or light bleaching from light being too close
(do you check your ph?)
most likely def would be iron
less likely manganese or zinc
have you been fertilizing? what fertilizer and how much?
I wouldn't freak out about it a small bit of yellowing in the new growth is common and not a big deal
and its very common in the first two weeks of bloom
but its hard to tell with the color distortion if its a def or just something that requires nothing
doing nothing would be better than doing the wrong thing so take it slow and easy