As I’ve actually seen such. And their flat-black coloration is very effective for night-ops. I guess you have to be in the Army to have had that sort of experience. [NOTE: 27 years 'in harness'. Airborne. Ranger. Mustang. And I've associates who say they've seen them too.]
What’s not-so-funny is that the name-calling, e.g., “knuckle-dragger”, effort to dissuade people from accepting what, even at first blush, is simply believable—it’s EASY to paint a helicopter ‘black’. And it’s an effort to make people ignore the very possibility. And it seems to work, amongst the ‘ignorant’ and/or ‘simple-minded’.
[Just because you're paranoid, doesn't mean they aren't out to 'get you'.]
Here in LA we regularly see unmarked Grey hekicopters overhead, Chinooks, Cobras, Hueys, Blackhawks, even on a CH-53. People say they’re movie props BUT WE KNOW BETTER. In Los Angeles, grey is the new black.
We were camping South of Death Valley. About 8AM two black helicopters passed overhead as we were hiking up a canyon. I pointed them out to my wife, Miss August, who offered, “Maybe they are flying to the place where they paint the numbers on them.”