Update 2/4/2014

The seedlings were growing too fast... so to slow them down I didn't fertilize for a couple of weeks. This was clearly a mistake. It made the leaves from the older plants start to yellow quite a bit, and not from over watering (which is usually the cause of the yellowing). I usually let them dry out and wilt a bit before watering. Anyway they obviously needed some food.

So we transplanted them into 18 oz blue cups with Pro-Mix seedling mix and 1 tablespoon of Tomato-Tone in each cup. The older ones are starting to do better.

We also opened up the windows so it'll be cooler and put two fans on them, to stop them from growing too fast, which sometimes causes leaf curl but also you get plants that need more space before you're ready to put them in the ground.
Anyway, after the potting up (even the younger plants got potted up to the blue cups), all of them are doing better. The younger ones are looking great, and probably are at the stage where they need the fertilizer (their cotyledons were yellowing.) Once the cotyledons fall off you can start fertilizing because those things are the source of nutrition for the young seedlings until they get old enough.

Here's some pics:

All the seedlings under lights. Most are doing pretty good, you can see the yellow leaves on a couple of the plants up front. There were some whose leaves got burnt from touching the lights, also recovering now that they are further. I read that the leaves can touch the lights, but apparently these lights are hotter than the ones other people use because the leaves that touched it fried to a crisp.

An older Brandywine Cowlicks. You can see the yellow leaves from being starved but it seems to get some green back now that there is food available. This is one of the worst looking plants of the lot. The root systems of these plants will take a little time to get back to speed again because during the potting up process some of them get damaged (which is all a part of the process)

An older Cherokee Green that is still doing good. This is one of the larger seedlings. Nice and short internodes, and stocky stem. Some yellowing of the older leaves. For each potting up, some older leaves got picked off so that we can plant the seedlings deep to get better root development.

A younger JD's Special C-Tex (foreground), very healthy and stocky  and an older Prue (background), which is supposed to be droopy and wispy. Prue and most of the older plants are still doing good. I was warned that Prue always looks like it's about to die but that's just the way it is. I noticed the same thing with Bull's Heart and Opalka, the other heart/paste types.