Chow_13answered grow question 3 years ago The cold would do it, anything below 15C starts to affect the plant and stunt it's growth.
Purple can be caused by many things and temperature is one of them. Also genetics play a major role.,
Cold temperatures will hinder the plants ability to uptake/process potassium so the leaves start showing sign's of a deficiency.
But the soil has enough in it, The plant was unable to use it so no action is needed.
Happy Growing