green stocks and stems turning purple

just was wondering if anybody knows whats going on with my plants. there about a month old, indoor, indica sativa mix, clones.

the top half of the plants are turning purple pretty heavily. just the stocks and stems and branches, not any of the leaves, at all. the leaves look very green and healthy. i was gonna put up some pics but its night time so they will have to wait till tomorrow.

any info would be extremely helpful.
thanks!

When I cloned my babies they did the samething and they are 45 dayz into flowering and are
Healty I think its normal I'm still a newb so I'm not to sure....good luck

Sounds like its getting too cold during dark hours. Ideally there should be no more than 15 degrees drop from night to day.

r u using nutes?? could b a N deffitancy??

im using advanced 3 part nutes. yea im thinkin it might be the temps, ill make sure i keep that in check. it seems like they might be coming out of it, cause the very tops of the branches going back to green.