What does this discoloration mean?

[Zandor]

You don't start feeding nutrients to seedlings. You start feeding nutrients once you are in the vegetation cycle. That starts once you have your 4th set of true leaves formed as a guide. Then you can use HID lights too if you got them. Use only fluorescents lights before that so yo don't get the inside temperature to hot.

[stickygreenlightsabr]

Cool. Well they are all starting to form their 5th set of leaves now.

[Zandor]

Cool. Well they are all starting to form their 5th set of leaves now.

Now you are in the vegetation cycle and you can feed them nutrients now.