For sun block, I wear a grey long sleeve T-shirt, instead of a black one, when hiking. I can feel the difference in heat absorption, but the ventilation does help immensely. The type of fabric, how it breathes, and the looseness seem key here.
I like Hawaii shirts best, they are light and loose, they sweat a bit, but the air flow through the moist air has a cooling effect, if I'm just out in the sun's heat, but when the sun goes down and it drops 20F or 30F, the t-shirt is warmer and the better all around configuration. That may have to do with Bedouin choices. They also must wear clothes for religious reasons. I'm not so sure about attitude, smell tolerance, perspiration helping the inside to cool, temperature variations, identity, tradition and other factors enter into the choice for comfort. I haven't walked even a quarter mile in a Bedouin's shoes.
Hands down my fellow choir, an all over tan butt naked is by far the most efficient outfit available. Nothing touches it. A skirt needs to breathe and it needs to be minimal short for better effect, ask any sundress girl.
Hmm, perhaps an aluminum material?...bags, thermal blankets, roofing materials, radiant heat barriers....
Jbee