It could be bad. Nitrogen deficency can do that. but it can also be a trait of the plant. I would say as long as the rest of the plant looks good, and growing well, it's most likely a trait.(I have some in my garden that look similar) But keep a check to see if there is any excess yellowing of leaves. if that starts it's a nitrogen deficency, simple just feed.
theres always one plant yoru gonna get thats the odd one outta the bunch... its kinda like a HAZE plant... your bud will have the same purple colas in it to... your lucky you could prolly sell this stuff for about 250 an ounce if it comes out correctly... its the trait of a plant called purple haze X1 well it gets purple in its early ages... great BUD... but it could also b lack of feeding but i think you got luicky.. plant loooks healthy
My plant has the same characteristics but it's doin awesome. Take a look in the picure gallery. have fun
I would have to agree with Dlayzdawg as it could be lack of N, another possible reason for the purple stem can be from cold temps. Maybe a pic of the whole plant would help to see the bottom leaves and if they are turning yellow and falling off.