what do people here do to keep their dark colored pots cool in the summer heat to avoid cooking the roots?
we have had a summer with many days above 90 and there is only so much room in the shade
Some people wrap the pots with white towels and wet them. Some just wet the pots and/or water during the hottest part of the day. Some have misting systems. Some move trees into the shade during the afternoon
If you have your trees in quality pots, or exhibition pots, obviously white paint is a very bad idea. White paint is okay for cheap terra cotta pots and plastic pots. Tape can leave gum residue on quality pots which could become a problem.
Greenhouse growers of potted plants,, will often have the pots in flats that keeps the pots tightly together. This way the pots shade each other. Several orchid growers I know leave a row of empty pots on the outside edge of the flats so that the empty pots shade the pots in use in the center.
Another trick, Nest a plastic pot inside a larger empty clay pot. The air space between the larger clay pot and the inner plastic pot with the plant will keep the plastic at ambient temp. The terra cotta clay will wick water and by evaporative cooling can be used to cool roots too if sprayed down occasionally on hot days. So inside a 5 inch diameter terra cotta pot set a 4 inch diameter plastic pot with the tree in the plastic pot.
I frequently get daytime summer temps above 40C - 100F. I don't cover pots or protect from hot sun. I don't see wholesale death or problems even with trees in black plastic pots. Maybe this idea of cooking roots is a myth?
White towels around the pots. Put them on in the morning before the sun hits the pots and after you've watered. remove them in the evening after sun has gone down. That will likely be more than adequate. Painting pots is time consuming and unnecessary. I typically cover up pots here in Va. when temps are forecast into the low 90's. I try to shade everything under a large landscape tree when temps are forecast to go over 95-100+ for more than a day or so. I don't do that if those extremes aren't forecast to last more than a day.