Here's a couple pics to help.

See the leaves closet to you?

On the left:

If you are talking about the very bottom two leaves that were first to come out when the seeds germinated, those are the "seed leaves" and that is normal.

Nefer is correct.

Your seedlings appear healthy.
Hard to tell what kind of light you are using naturalstuff.
Although you may be using fluorescent lighting, the yellowish color I'm seeing could be refraction of light off the plywood. If it isn't from the plywood, yellow light usually means incandescent (standard house bulb) light which isn't a good source for the seedlings.

Fluorescent = GOOD
Incandescent = NO GOOD

Paul B.

Paul, it is a flourescent light, it does appear yellow with the wood reflection. Although I can see a slight color difference between florescent screw in bulbs and the regular flourescent tube bulbs.

Are the bulbs rated "Daylight" at around 6500 Kelvin?

Where would I find that out?

Most likely on the packaging on the tubes it's printed on the glass.

All you need is the cheapest bulbs at Wal Mart unless you plan to grow them entirely under lights.

John

I believe you want cool white bulbs as they throw more light than warm. But cheap is fine; no need for expensive grow light flourescents.

-J

I believe the cheapies are, in fact, cool white.

John

I agree w/ both John and...John. :)

Paul B.

Might be excess nitrogen

I'm not sure by observing photo's - but if the 'first two leaves' you are referring to are the first leaves to emerge from the seed, then I believe the yellowing is perfectly normal. Those first leaves are the embryonic leaves called the 'cotyledons'and are the first food source for the embryo and will eventually fall off once the 'true' leaves appear and begin generating food for the plant 'photosynthesis'

Another possibility: Leaves will begin to yellow after time if there is no source of nitrogen. Potting mix may only carry the plant so long and you may need to begin fertilization.When you begin to fertilize - go easy as excessive fertilizer can burn leaves or produce a too rapid growth. Personally, I wait till the leaves begin turning yellow before applying liquid fertilizer, as to not encourage a too rapid growth indoors.http://en.wikipedia.org/wiki/Cotyledon

I added diluted Miracle Grow plant food to 3 of the cells out of the 5 pepper plants there. Would you believe that I can see a difference in those 3 already! After 3 days!? They are slightly taller and feel sturdier. I'll transplant into better soil next weekend.

Pot bound is another reason that leaves turn yellow

"Pot bound is another reason that leaves turn yellow"

How do you explain these nurseries that have the plant in the csmall cells for 2/3 months and the plant is as healthy as you can get?

The yellowing is not normal but I wouldn't worry too much about it unless the leaves wither as well. I had a lot of newer growth leaves yellowing that I thought was due to overwatering but the plants remained off-color even after a few weeks until I transplanted them. Then they turned normal green within a few days.

Sometimes I suspect that there are mixing problems with media mixes and other times I've used a fungicide to prevent damping off and produced severe yellowing, likely due to the fungicide carrier compound. It has always corrected itself with time. If you are concerned about the plant appearance use a foliar spray of chelated iron. It will produce dark green leaves in a short time.