Yea, I have a few plants with purple stems. They're good healthy plants. Relax.
There we go...focusing on the new growth is a good way to tell if you have fixed a problem...from what I understand of purpling is, when the rootzone temp are too low, the plant has a hard time uptaking potassium and phosphorus, also PH imbalance will cause the plant not to uptake certain elements.I'm not 100% sure on the stems of a seedling, but I have grown several strains in the same container with the same soil,water and nutes...some purple.. some don't. I would focus more on your top sprouts and their coloration and vigor.
most seedlings have purple stems....i've got quite a few purple stems on my new seedlings, my temps are never over 80* never under 73...they are only a few days old, and i think i overwatered them to begin with...maybe its just genetics, i've seen plenty of weeds outside growing, that have random purple stems...