You're half-right, Zeppy. The physics of color are more complex than we are giving them credit for here.
The black square you posted was created by the computer ordering the monitor to light up none of the pixels in that area. You can test that by filling up the entire screen with a purely black image, suddenly switching off the monitor, and then comparing the two "blacks" with each other. They will be identical, excepting for whatever distortion results on the monitor screen as the result of being energized. In this particular case, then, it really is an instance of "no light," and you would owe me $50.
However, that isn't the universal explanation for blackness. The "color" black is actually any kind of pigment which, as you would point out, reflects very little light. You can see this in print media; for instance, a sheet of paper that has some text printed on it. The darkness of those dark marks is not the absence of light itself, because we know that just as much light is striking the dark parts of the paper as the white parts. Rather, the darkness of those dark marks is the result of the absence of reflected light. Had you used the example of a printed sheet of paper, you would have won your $50 bet.
Yet there is still more complexity to consider. In cases where there truly is no light available, then everything will appear black regardless of how reflective it is. This is the general case of "no light," of which electronic monitors are a specific example, and, had you used the example of, say, a darkened room, you would still owe me $50.
Another fundamentally different type of "black" is nothing, which invariably shows up to our eyes as black.
There is plenty of reading on the subject, and anyone interested can begin at no harder a destination than Wikipedia. As for you, Zeppy: Because I am so beneficent, I release you from your debt. =)
