@Alienwidow
Hydro right?
I will get flamed for mentioning this, but stoner myth has it that adding ice the last week of flower Will cause a stress response to produce anthocyanins. Anthocyanins are a type of flavonoid, and is responsible for red, blue, purple ect in flowers.
The catch is the genetic has to be able to produce anthocyanins or you are spinning tires. This is why flowers are cloned in flower shops. That specific plant produces a lot of anthocyanins, giving it it's vibrant color.
So I would say find a strain with known anthocyanin production and then figure out a way to my the plant express itself. Cold temps, both air and water. Purplemaxx or a purple supplement. Drought. Light dep
My 2cents