Why are my seedlings stems going dark purple?

[Phillybonker]

Is it stress from stretching or cold nights (10 C)?

Or is it too much sun? I put most of the seedlings out in direct sunlight as soon as I could, after they showed their cotyledons.

Sorry I can't upload a photo for some unknown reason.

 

[Phytoplankton]

They’re gonna be fine, don’t stress, happens all the time.theyll grow out of it.

 

[BAKIND]

Could be a sign of stress from the cold nights, but it's something they can overcome.