Purple streaks

So I'm around halfway through my first grow, obviously don't know everything/much but was just wondering about these purple streaks:

They have become much more prominent since I put the plants outside, mostly on the newer growth and has started showing a lot on the stems that the leaves are on and I was just wondering what it could be? Thanks in advance to anyone that can help out.

that can be strain related, or more likely due to the cool nights
Dr. Jekyll

it's a rare disease that will likely kill your entire family, best to flush it with gasoline then ignite it.
Mr. Hyde

Phosphorus or Mg

I"m with dr jekyll and mr. hyde on this one, I dont believe it to be a nutrient deficiency

in veg. all good. some do some dont. dont listen to the cal mag thing right now. ph fluctuations, colder nights etc can do it. if you tried to fix it, you would risk harming by misdiagnosing...most likely

I got lots of purpkle stems

Too cold of temperature can cause a Phosphorus uptake problem. Simple.

Sweet as, cheers guys. My guess was from the cold nights too. It's dropped to 6 (Celsius) a couple times since they've been outside but at least it's nothing serious. They're still getting a good amount of sun during the day so will see how it goes.