why would the cotyledons be turning yellow? they are on the cherry type tomatoes but not all of them, they are only an inch or so tall. sun gold and sun sugar plants, never had this happen before, rest of plants seem to be ok,i have both red and white LED lights could it be they dont like the red lights yet? if so why arent the rest turning yellow? lol i havent watered any seedlings yet, they all seem to have enough yet from planting, i go by weight of each small pots as when to water, thanks tom

If you're watering from the bottom, perhaps the roots on those have gone the deepest on all of your plants, and there is a lot of moisture at the bottom of the container. I'd try repotting just one, with dryer mix, as a control.

It's a good thing that you do not have white cotyledons, as those plants never make it.

Sometimes with older seed I've seen the cots turn yellow as the plant is struggling to find enough nutrients to get into their true leaves.
Are they big enough to give them a little liquid diluted N ferts?

they have only been out of the ground a few days. i havent even watered them yet. only the water that was put in starting soil when i planted them, i germinated them in baggies.

You may be right that it is your lights. Plants seem to react differently to them. Of course I don't know that this is the reason but it is worth investigating.

I had the same problem with the tomato rocket seeds from the dollar store.
They come embedded in a growing mat I assumed had fertilizer infused.
All the plants were anemic so I had to keep spraying them with a fertilizer.
out of 25 plants only 2 survived.
I started other seeds in seed starting mix one month later and the original plants finally caught up to those in size.