The first one would be a ham-fisted reference to a black-body reference body for determining z for extra-galactic objects. This is not it - nor is a lens cap!

The first one would be a ham-fisted reference to a black-body reference body for determining z for extra-galactic objects. This is not it - nor is a lens cap! Black as a colour - nonsense. What we perceive as black is brought about by maximal absorption or minimal emission of visible light by a body. Frankly it's all based on what a wobbly sphere of cells can and can't detect, so you could have something that pounds out UV, IR, microwaves and gamma radiation and still call it black.