Stems on my Red Bell Peppers are purple? Is this normal?

[Hydroking]

I have a hydroponic drip system that I built a few weeks ago and so far so good. I have red bell peppers and they are approx 2-3 weeks maybe. I have never grown before so I am wondering if purple stems are normal? or maybe a nutrient deff?

[rainbowgardener]

dark or purple stems on peppers, especially around the nodes is pretty normal. Someone posted a picture of it here once, but I couldn't find it.