That's very interesting. I never knew that they turned red in cooler weather.

When I lived in Orange County, CA, we had loads of these spiders in our front yard. Never once had trouble with them coming inside or biting anyone, they seemed very shy and kept to themselves, and I personally fell in love with their demeanors, unique looks, and vivid colors.
On several occasions, I was rewarded by watching the generations of these spiders come and go. The first mom spider made her home on top of a pad of flowers on my mom's heliotrope bush--which looks like what this one is sitting on, except on a leaf. One day her belly started getting bigger, and I was excited with anticipation at getting to watch new life enter the world.
She got bigger over what seemed like a long gestational period for a spider, perhaps 3-4 months though my memory's fuzzy. I noticed that her abdominal color change, from green to pomegranate-seed red, correlated with how much fuller in figure she got with eggs.
Now it never...really...got cold in Orange County. It really just never does. So I actually theorized that the color change was sort of like the arachnid equivalent of stretch marks.
The most convincing bit of evidence came the morning when I left for school and she had laid her eggs--she was slim and green again! But as time wore by, if I wasn't able to swat a fly down to feed her, the mother spider wouldn't eat...unless food landed on her nose. And it was her dedication as a mother to her babies that saddened me as I watched her get skinnier and yellower, until eventually her babies left the nest...all except one. The mother would then retire away to die peacefully after living a productive life, and one of her many daughters would inherit her "pad."
The last time I checked, this same pad of flowers had been inherited six times, all by daughters from the same family. I always made sure to find the corpses of the dead mothers, and I even made a small family plot I buried them in.
These really are amazing spiders, and it doesn't take much to get attached. Now living in the California high desert, I miss them dearly. Noooo, instead, I get DESERT RECLUSE SPIDERS IN MY BEDROOM! YEEK!

A fine older gal she turned out to be.

Except I said older not colder. The only ones that I've seen turn the reddish color are the large females (I'm assuming these are females)....toward the end of their lifespan.