The dot screen of printed matter. Look closely at a newspaper photograph and you find no grey at all, only black dots of varying size on white paper; from a normal distance your eye averages them into tone.
In colour mode the picture is split into the four printing inks, cyan, magenta, yellow and black, and each gets its own grid of dots turned to its own angle. The angles matter enormously. Line four identical grids up and they interfere with each other, producing the ugly rippling pattern printers call moire. Turn each one to a different angle and they never line up, which is why commercial printing has used those particular angles for a century. The four are then combined the way ink actually stacks up on paper, each one taking light away.
Monochrome mode screens brightness alone, with a round dot, a line, or rings. Each cell reads a small average rather than a single point, so its dot reflects the whole patch.