Let me expand on my abrupt comment... no offense Bozon.
The air is made of particles, and these particles have a reflective and refractive index to them. It may seem invisible right in front of you, but over a distance (even on the clearest day) these particles are obscuring your vision, like looking through a very thin cloud. This is why you don't see black outer space during the day... sunlight is lighting up all these particles, molecules, etc, and making them a significant ambient light source. Blacks become greys, blues become lighter greys... whites even become grey. Even an all-black aircraft will become grey. An aircraft sitting on the ground will have almost black shadows on its underside, but an aircraft in flight has very very soft shadows on its underside... the air is effectively a light source below (and all round) the plane. It's not a matter of color, either. The atmosphere has a way of desaturating colors.
Artists use a technique called
Atmospheric Perspective... by lightening the values and desaturating the colors the closer you get towards the horizon, you convey a greater sense of distance within the 2-dimensional format.
What you
are seeing is intensity and contrast. If a light-colored plane is moving against a very dark and consistent background... say, large grassy fields, then spotting that plane is much easier. Against lower-contrast backgrounds? well, if you see it, you're lucky. Look away for ten secoonds and see if you can find it again quickly.
John9001: there is a factor here that you are not figuring... you are absolutely
expecting to see other planes over this field, so it's no surprise to me that you spot them so easily. But enroute is another matter, altogether

I also would have to ask what kind of background you saw these dots against.
I've had formations of C-130s pass a couple thousand feet below me while enroute. Big planes, huh? But with their camouflage and speed, very difficult to see until very close, and my SA is no worse than any other pilot's. They paint those planes green for a reason. If it didn't matter, and they turned into black dots at ten miles out, then they would save weight, time, and money by not bothering to paint them. Why do you think most aircraft camos these days are variations of grey?
Bozon: the experiments you refer to have been tried on all kinds of things... tanks, ships, airplanes... even buildings. By covering whatever with a grid of lights whose
intensity matches the
intensity of the air behind it, you effectively blend it into the background. Nothing to do with color.
Anyway, Pepe, I agree with you. I'd like to see the distance dots modified if possible. And yeah... what the hell is the KI-61 camo supposed to "blend in" with anyway, a car dealership?