Sun bleaching?

hi there macky, to me it looks like you're using something called "potting soil" for your medium. This is will cause this issue, why? because potting soil is peat, which is basically not soil at all, in fact it's a soiless medium. Soiless means you're missing out on nutrients for example calcium and magnesium, which will lead to the seedlings showing signs of magnesium deficiency for example like what you're seeing here. So you need to add calmag, and actually you'll need to have a full on nutrient schedule going forward. I could be wrong though, but probably not :-) hope this helps ! 🚀