I am especially intetested inanodized and blackened aluminium and its alloys.
Theoretically, blackbody is supposed to absorb all radiations impinging on it, without discrimination, be it visible or invisible, and similarly, emit a wide rande of radiation upon heating, exactly given by planck's black body radiation equation (the forerunner of quantum theory!). If the effect of bandgap is manifested as sudden/abrupt change of absorption or emission at some specific wavelength, then the material is indeed deviated from ideal blackbody relation. Remember, blackbody is a very specific term- shiny, black volcanic rock aren't blackbody in that sense since they reflect (at least in a specular manner) a significant fraction of radiation that is well within visible range.
Metallic Aluminium have zero bandgap, but its surface oxides and coatings likely not. It is likely possible that, above the wavelength, and hence below the photonic energy of bandgap of that coating, the coating is transparent to the radiation, and metallic reflection would ensue. Above bandgap energy and below wavelength of coating's bandgap, a significant fraction of light would be blocked, so we might have red/yellow/brown etc. colors if scattering of light from surface (and other choromophore from transition metal/conjugated compounds are not there in coating)is not much present. Hoever, above metallic plasmon frequency near UV or soft X-ray, the metal would become transparent, and penetration of radiation through the thin coating would only keep rising once radiation is energetically high enough.
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