temps are not the cause of the purp its caused from a potassium def. which all purp strains have but only into late flower its nothing to worry bout its a good looking plant and you gotta think each leaf is like a solar panel you cut them off your going to shock the plant and lower its energy production which will just slow it down only time you should thin a plant out is when the leafs are dead or are shading other plants and also when they are in flower and you have poor air circulation