If they have identical or close enough emissivity it is directly proportional to heat absorption, as given identical amounts of time in the sun and air flow, temperature will almost entirely depend in absorptivity, and emitted infrared is proportional to temperature^4.
Black bodies emit and absorb perfectly. These probably all have an emissivity that’s lower than a blackbody, and very close together, while absorptivity is related to the color of the shirt. So this test is actually fairly indicative.
If they have identical or close enough emissivity it is directly proportional to heat absorption, as given identical amounts of time in the sun and air flow, temperature will almost entirely depend in absorptivity, and emitted infrared is proportional to temperature^4.
Black bodies emit and absorb perfectly. These probably all have an emissivity that’s lower than a blackbody, and very close together, while absorptivity is related to the color of the shirt. So this test is actually fairly indicative.