Yes, all of that is obviously true between shirts, the question is about shirt color, which is almost entirely down to the pigments used in fabrication. In which case it is entirely due to the absorptivity, emissivity, reflectance, and opacity, of the pigment.

This isn’t an active area of debate, it’s an entirely empirical question or a hard modeling problem per shirt manufacturer. All of this is very solved science, and has become “an engineering problem”