SOIL why am I purple?

[jimicloudstuff]

I can't find anything in sick plant guide that looks like this. Maybe phosphorous?
The same strain went purple outdoors but it was cold, I've never grown it indoors. Temps may have gotten down to 55 f but no lower.
My concern is that it is some deficiency. It is starting to show up on my other plant, which so far has been perfect.
1st pic today, other one a week ago.

Details:
5th week of flower. Soil, dry amendments. Tap water, ph to 6.5. Plant was topped with a roughly 0-6-9 dry blend, lime(ca), and epsom(mg) about ten days ago.

I should say that so far the purple leaves seem perfectly happy, but they weren't purple three days ago.

Any Thoughts?

Thanks in advance.

[Gingerbeard]

jimicloudstuff my new farming friend. You are coming to the autumn of you plants' lives. The purples are absolutely normal. Wonderful. Purple! You may also come to yellowing fan leaves. Normal as well. Remaining nutes and sugars are being sucked from the fan leaves. Could be a purple strain? Could be environmental conditions. Just take a picture every day to watch the progress.
I like this question because I get to show my prettiest plant yet. Don't tell the others I said that.

[dropinbiking]

55 is plenty cold enough to make colours come out.

[jimicloudstuff]

Thanks guys, good to know! 1st grow indoors, I like being able to watch em up close. Very nice @gingerbread .

[FunkyButtLovin]

With a name like jimicloudstuff I'd expect some purple. As dropinbiking said, 55 is more than cold enough to bring out purple in plants that have the genes.