Yes, red leaves can be due to sun stress, or heat stress.
Does anyone know if dryness can possibly cause the leaves to be red? Even though my pool deck is screened and shaded by lots of trees, a few of my Hoyas leaves have lots of red coloration. It hasn't been overly hot yet but my plants have been extremely dry because we haven't had much rain in a long while ... and I've been lazy regarding watering regularly.
