I've been thinking, imagine you have a room, a light bulb at the top and you hold your hand up off the ground. Of course, there will be a shadow under your hand and no light will have access to that area, since the hand is blocking the light (the electromagnetic waves). So why am I not seeing clear black, and I'm seeing the dark version of the floor color, the shadow is kind of black transparent, gray... Why am I not seeing complelety black, or maybe the light reflects to the walls of the room and still happens that some very little light access the shadow area? When I move my hand closer to the ground, the shadow goes darker and darker.
An alternative way to look at the situation. Imagine you were in space, with the sun shining on you as you traveled along in your spaceship, with its lights off. If you passed behind a planet or a moon, in its shadow, you would experience darkness. How much darkness?
a. If your spaceship was between earth's moon and the earth, you would be in the shadow of the moon, but the side of the earth you were looking at would of course be in daylight. Then, your darkness would only be partial as the earth would light up not only the dark side of the moon, but your spaceship.
b. If, as you passed behind the planet or moon, in its shadow, there were nothing nearby in the direction of the dark side except your spacecraft, then it would be virtually absolutely dark.