I know almost nothing, but I wondered if the color could be genetic (Wild guess)? Structure looks solid. They are just barely old enough to be ready for any food... so I rather doubt deficiency.
Smartphone app with light meter will get you in the ballpark so you aren't completely guessing on the light. I would shoot for about 10,000 LUX at the leaves and start working that up to 50,000 over the next 2-3 weeks.
I have no idea, but some issues plants of mine had seemed to be from a virus, like TMV. Parts of leaves were affected with an odd pattern and they sometimes would bend in a weird way, but they were otherwise healthy.
For the record, I don't think this is TMV or any virus, just some weird stuff a young plant might be doing. Those patterns don't look like anything I'm familiar with, and some plant or another that I've grown has suffered just about every deficiency possible.