The emissivity of a gray body is constant but is considered to be less than 1. Since the black hole is considered near perfect black body but not a perfect black body its emissivity will be less than one hence can it be considered as a gray body?
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A quote from this paper:
At the precise location of the event horizonthe Hawking radiation is blackbody radiation. However, this radiation still has to traverse a non–trivial,curved spacetime geometry before it eventually reaches an observer and is detected (e.g., an observerlocated at asymptotic infinity in an asymptotically flat spacetime). The surrounding spacetime thus worksas a potential barrier for the radiation, giving a deviationfrom the blackbody radiation spectrum as seen byan asymptotic observer. The relative factor between the asymptotic radiation spectrum and the spectrumof blackbody radiation is dubbed the greybody factor.
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1$\begingroup$ I'm not the downvoting party, but answers that merely provide a link to another work are generally not considered good answers. If you summarize the primary points in your own words the result might be different. Another option is to include your quote in a comment. $\endgroup$ Oct 25, 2020 at 14:59