It's probably a combination of the surface being black in colour (charcoal), plus a surface texture that absorbs light. It brings to mind the way feathers and

It's probably a combination of the surface being black in colour (charcoal), plus a surface texture that absorbs light. It brings to mind the way feathers and insects often have brightly-coloured parts that aren't due to pigment but rather the microstructure preferentially absorbing/reflecting specific wavelengths, giving a colour. https://en.wikipedia.org/wiki/Structural_coloration https://en.wikipedia.org/wiki/Structural_coloration Similarly, I wouldn't be surprised if the microstructure is tuned to work best (lowest reflectance) in the visible light range. EDIT: limited wavelength range also applies to other "super-black" materials https://en.wikipedia.org/wiki/Super_black#Technology https://en.wikipedia.org/wiki/Super_black#Technology