Traditional security printing methods meant that stamps were limited to a few colors at most. That changed in the late 1960s with the first use of “process color” in U.S. stamps.
Process color combines tiny dots of just a few inks—usually cyan, magenta, yellow, and black—to create a full range of color. This allows for far more varied stamp designs, including the use of color photographs. But the first process-color stamps used a relatively coarse “dot screen,” and often appeared murky or soft. Today’s examples are much improved, although engraved images will always be somewhat sharper.
Two different methods are used to print U.S. stamps in process color—gravure, in which the dots are recessed into metal plates, and lithography, a chemical process.