Looking a bit yellow

My giant white habanero, Trinidad perfume (and orange habanero, first time growing) always do it. They always colour up again quickly once they get moved to the polytunnel. I panicked the first time I saw it. Now I just let them get on with it. No idea why some react like that under the lights.

No, the Trinidad Perfume is uniformly lime green. I just went downstairs to check, and it looks greener from on top than it does from underneath (the seedlings are on a shelf above my eye line). Also, I think it only looked so pale because it's right next to the Hungarian Black, which has purple cotyledons and purple-tinged true leaves.

My lights are white fluorescent, so maybe they don't affect the chillies the same way as your fancy LEDs?

Overwatering, maybe? It's very easy to overwater peppers when they're small. I've got a few that weren't looking great, leaves very pale yellow, now the compost is drying out they're greening up again. Some varieties seem more prone to overwatering than others.

I'm generally very sparing with the water - but the compost I transplanted it into was rather soggy as the bag had been out in the rain, so maybe that's the problem? The tips of the leaves are already looking a bit greener, so I'll let it dry out and keep my fingers crossed.

Thanks, everyone, for the help!