What are my seedlings trying to tell me?

[RomanX]

All of my newly sprouted seedlings (just yesterday, I "freed" a few from their "helmets") have faintly purplish stalks (so light, it's almost lavendar). They just came up last Saturday, so only have cotyledons. Eight different varieties, 25 seedlings, all the same.

Last year, my seedlings got purple stalks when they had several sets of true leaves. After I was advised (here) that this was caused by a potassium deficiency, I promptly fertilized them more: no more purple!!

But this is too soon to fertilize yet - or is it?? What should I do??