Purple Branches?

This is my first grow this year and I think they are looking beautiful. I have a total of six plants that are at least 6 to 7 ft. tall and all are sativas but one..They are 2 different strains which I don't know of and I got from bags. On my one Indica the branches have turned PURPLE for some reason and I am worried. I live in illinois and supposobly we have the best soil so I haven't used any fertilizers but did use miracle grow bloom booster about a month ago. They have already flowered but it has been purple since for at least the first month of its life. I put seeds in the ground may 31st exactly. Can you explain to me why this is.

I will have pics soon..

Its no big deal. Alot of them have purple

yea my last grow some of the branches of my sativas were turning slightly purple but i think it was because i wasn't properly feeding it

dont worry about it man they turn purple its alright usually caused by a cooler night doesnt hurt anything just makes em look perty