Red stripes to appear on the stems

There is actually many reasons behind stems turning red/purple. 1) Genetics. Some strains are breed this way and there is nothing you can do about it. A lot of new stuff coming out look almost black with how dark they get. 2) Phosphorus deficiency. The first signs of phosphorus deficiency is that the stems of your leaves start turning red/purple. 3) Magnesium deficiency can also lead to red looking stems. 4) Cold temps in the grow environment increase the Anthocyanin production which is a purple/red color. As far as what you are dealing with. Nothing to worry about now, keep an eye on it and if your getting alot more purple/red colors in a lot of the leaves then you should reach back out with some pictures here. Hope that helps.