Red on leaves and stem

Hi alll,
I have noticed some red on the leaves and upper stems of my plants. Anyone know what this means?
Thanks!
your bud

yo I have young plants and the newest set of leaves looks purple. same problem? i dont use ferts yet, how do i fix phosphorus?

Young plants and old plants alike can have reddish or purple stems. While this is a sign of phosporus deficeincy, it can also indicate a pH imbalance which is locking up some nutrients, or could be a genetic expression of the plant. In the young plants it is usually not an issue. In plants that have been flowering for some time I would suggest checking and adjusting the pH first, and then consider changes to the nutrients.

Hmm,
My plants are slightly over 2 weeks into flowering. They look very healthy except for the red up top. I am starting a 10-30-20 fert today. If it is a problem, that would take care of it, right? Its good to use that mix during flowering anyway, correct?
Thanks guys!