Leaf looks on max healthy green fo bottom part of plant, aka most matured, they are not overfed from this view.
Veins could be some magnesium lack, Epsom salt easiest way, or just small temperature swing, genetics, could be many things, doesn't look like a thing to worry at least for now ..
All the Best !!!
Enjoy the grow of the canuk cookies. Might want to switch to 20/4 lighting. Plants need a rest as well. Plus it is a lot less stressful on equipment running non-stop. Good luck 🌱🌱🌱