Printed full-color images are often made from dot patterns called halftones. From a distance, they produce the illusion of smooth shades and millions of colors, but made from just four colors: cyan, magenta, yellow, and black. Posy’s video offers a brief overview of the technique and a series of close-up dot patterns zoomed out to see their full images.
Printing and silkscreening produce full-color images by separating colors into cyan, magenta, yellow, and black, then printing them a layer in a dot pattern. This artist does the same, only using markers on transparencies. They didn’t bother with black because CMY is enough to create most colors, just without much contrast.