In the season one He-Man episode "Eternal Darkness" Prince Adam and Teela journey to the Crimson Valley to investigate some explosions that Orko has heard. Here we can see that once again the artists of Filmation have created another beautiful image showcasing Eternia's weird locations! The "reddish cast" as described by the script is evident across the land, and the director has even made sure to include a sun, requested in the script. If you look at the map of Eternia earlier in the episode Prince Adam points to where exactly on Eternia the Crimson Valley is. Maybe another post for another time?
(click on the image to see it at full-size)