Tropicanna Cherry XXL – Purple leaves: genetics or problem?

The red is genetics or cold temps at night, the latter can contribute either way. underfed or out of balance... possibly light too close since it's relegated to the top. I'd try to fix that if the rate of deterioration means the canopy won't hold up until harvest. too much p/k can cause chlorosis at the top and skinny fingers on leaves, which seems to be the case, but leaf symptoms are not discrete as to cause. Match degree of adjustment to rate of progression... be conservative. always easier to add more nutes than take away.