It's tough to know for certain what is happening. Perhaps it's a case of edema? Don't know as the image doesn't clearly show the detail.

If nothing else, the newest leaves look fine.

A wise guideline to follow:
While raising seedlings, if one is off-color and looks obviously "sick" it's wise to remove it before others are affected -- that is, if there's any chance of the problem being contagious.
(In this case, I'm unable to say if that's true or not.)

Thanks, Jean. I went ahead and removed that seedling just in case. I planted three in each starter pot anyway, and one of the other seeds is just sprouting in that same pot, so I'll see how it does.

red .... which on green can look brown..

can be insufficient light...

how far are you lights from your seedlings ... 2 inches max.. [why is the plant leaning to one side... stretching for light???]

and how many lights are you running ...

lets see what the next set of leaves look like ... [they look pretty nice.. as small as they are] ..... before we worry too much ... if you are doing this in a window.. cold damage might be possible also...

your pic is out of focus.. and not well lit.. to 'see' the actual leaf surface.. so its just a bunch of guessing ...

ken

ps: whats all the hard water stains on the cell pack ... water or fert??? .. maybe you burned them with a fert drench????

Ken,

Very observant! The stains are indeed from fertilizer. I use 1/4 strength fertilizer once per week; not too much, just wet the medium off to the side of where the seedlings are emerging. Lights: Now I use one T5 running down the middle of the tray. Its about 2.5 inches off the tallest seedling. The ones along the far edges of the tray do bend inward a bit to get at the light. Originally I had one 60W incandescent bulb (albeit one designed as a grow light) but that wasn't doing the trick. Plus it was too high above the plants and they got a bit leggy. I wonder if I still need more light even now.

Here in MD we have a lot of stink bugs and the latest issue is they get attracted to the grow lights and end up grabbing on to the seedlings, thus bending them down and damaging the cotyledons. If it isn't one thing its another.

Anyway I already cut the red/brown leaved plant and got rid of it just in case. Other than the seedling the stink bug damaged, the rest all look healthy at the moment.

Will