The lighting for a seedling is usually 24/0 with CFLs.
Although it CAN be 18/6, with stronger lights.

The yellowing...I don't know. I've never had that problem. The only problem i've ever had with seedlings is stretching. And that can be fixed with a fan, and about 2 weeks time.

But I dunno. I've never experienced yellowing before in a seedling. Perhaps your lights are too low, or you may even be over-watering. That's anyone's guess...I dunno. Never had that problem.