I recognize the difference between a black/dark car and a light/whits one here in this Arizona heat. You see a person in a black car and it is assumed that that is a recent arrival from another state. Stepping into dark rubber shoes left in the sun, the difference between dark and light granite in the sun, all of this makes the dark material seem foolish. Black adsorbs the heat and white reflects it. The difference is dramatic. I feel the difference wearing my black t-shirt instead of my light color one.
The type of materiel allows the air to breath through, the bigger the holes the better ventilation.
The wet cloth cools, but if it is soaked in hot water it gets hot. The water in a garden gets hot in the hose under the sun, and black hose is best for solar hot water systems, this is what a wadded rag does. You unwad it and hold it to the air to cool it. Does hot water evaporate and cool better and quicker, maybe, but does it get cooler quicker? No, it is farther to cool down hot to a lower temperature.
Loose thin clothing helps the ventilation, there is a cooling effect, the skin picks that up. It is obvious. There is an evporative effect. You don't paint an evaporative cooler on your roof black, it needs to blow cool air.
I just don't see the logic of wearing black on a hot day. A black hat is noticeably hotter. Black clothing helps keep people warm.
I heard about these people in black years ago in a desert in which it turned cold at night. I have heard of a habit of traveling in the cool of the night for some people, I know that some deserts are cool and cold and perhaps these are the places that these nomads developed the use of black absorption instead of light reflective. They are compelled to wear a full covering as Muslims.
Skin is best, shade is better, an umbrella and naked works better. I can know this when the clouds come over, when wearing a brim on my hat. I can know this, as a light breeze hits my body on a hot day, and what happens on my back where the backpack covers my body, and the sweat doesn't evaporate and cool me. We are geared to be naked in the heat. Our skin learns to accept more sun, if it gets a tan slowly. Some races are acclimated to sun better than others. Some are acclimated to lack of water, cold or altitude, too. We can rest during the heat of the day in shade, it is natural to do that.
Nothing logical, nor anything in my experience has shown me that it is better to wear black clothing in a hot desert. I wear a light color umbrella, or hat.
Jbee