Looks purple to me.
So it is actually KILLING the affected tissue? You're certain of that? Because if it isn't killing the leaves... I have a theory.

The rest of the plant looks healthy.
Have you ever seen partial albinism in cannabis? The plants show random patches of white tissue. The fact that cannabis CAN be variegated makes me almost wonder if what you are seeing is simply a purple variegation and it is only coming out now because of temperature changes- have you been dropping into the low 60s at night, or lower?
In the meantime, DO NOT PINCH OFF AFFECTED PARTS!!!! Those are bud sites. You'll kill your yield.
Do you know the strain? Please post it so I can quick have a look and see if any of its near ancestors are known to carry purple traits.