Purple Stem?

So I just started LST on my White Widow plant under a 250w MH light. While I was away for Memorial Day weekend a big section of the stem turned purple. The plant seems to be healthy because there has been growth. Any insight to the cause of my confusion would be appreciated.

just the plant. i had white widows earlier this year and they had purple stems. i think its pretty

If not genitics of the plant, purpling stalks generally are caused by temps below 55F or phosphorus def.

To rule out PH related issues complete a soil runoff PH test.......
with PH corrected water (6.5-6.8PH ) pour enough water in the pots so the water runs out the bottom of the pot ...test the PH of this water....
If the PH reading is out of optimum range 6.5-6.8 PH, you need to flush your plant.
Flush with PH corrected water, till in optimum PH range, 3 times the volume of the pots rule of thumb but may require more
EG: 1 gal pot = 3 gal. flush
add 1/2 strength nutes to the last gallon of the flush.

The purple stem must be in the genitcs because more and more of the stem is turning purple and the plant is doing fine. My pH tester is with my buddy grower so I will have to retrieve that and check everything again.

This happened to my first plant. Reason was big temp swings, from 50-105 for a few days.

From what I was told this is a bad sign of plant stress. My plant seamed fine for a time(day or 3), but then quickly stopped maturing. I was told that the stress would push back my harvest time about 2 weeks...just sharing what I was told, I am a noob...I hand out salt grains with my advice, lol!

The purple stems are very common.
It's usualy a stress response and most plants will grow 'just fine' with them.
LST can cause this, as do topping,fimming,soil issues, temperature swings, acts of god and so on and so on.
I see it as a yellow warning light : something's up!
As long as you're sure about the cause, no need for alarm.

I believe it means the plant is in full sun/light....