TV question

Not about TV shows or anything like that, but about the actual TV set.
The picture on TV sets are made up of tiny squares about the size of the head of a pin. The TV screen has more of those squares than is usually used, for whenever you are watching a letterbox show.
All of the TVs in my house(even the bigscreen) have extra squares in the middle of the extra spaces, and those squares actually have color and have, I assume, more of the picture that is on the screen.
My question: Does anybody else have that? Does anybody know what purpose those extra squares serve?

The extra squares are black background.
They were once grey, considered “Neutral”, until someone realized they were lowering contrast.

The problem is the 3colorgun scheme- 3 is not a good number for packing dots.