Plant Could Turn Purple?

I heard that when outdoors to not harvest your plant and let it last through a couple of frosts. This way it will start to get a purple color to it. Is This True or just a hoax?

its true the cooler temps near the end of harvest can bring out the purple in some plants.

Yeah I've seen it happen. Even temps just over frosting can cause some purple color. Last year my plants went through 3 light frosts before i harvested. Interestingly, the parts that were the most purple had bigger trichomes. Apparently the stress causes the plant to produce more resin. Just be sure to watch for hermies. After the 3rd frost 1 of my plants hermied from the stress. Only a few seeds in a local area though so no big deal.

if you want plant a purple colour give some beetroot juice