“The amount of heat gained by a Bedouin exposed to the hot desert is the same whether he wears a black or a white robe. The additional heat absorbed by the black robe was lost before it reached the skin.”
Bedouin robes, the scientists noted, are worn loose. Inside, the cooling happens by convection - either through a bellows action, as the robes flow in the wind, or by a chimney sort of effect, as air rises between robe and skin.
Thus it was conclusively demonstrated that, at least for Bedouin robes, black is as cool as any other colour.
https://www.theguardian.com/education/2006/aug/15/research.highereducation
But t shirts don’t work like Bedouin robes.
Only if you don’t know how to sandwalk, Outworlder.