Two-tone paint jobs were around long before the 1950s. Before "streamlining" and envelope bodies came on line, two-toning often took the form of fenders, valances covering the frame, and perhaps some other areas being painted black, the remainder of the body being in another color. By the 1940s, the two-tone convention was that the "greenhouse" -- the part of the body above the "belt line" (roughly at, or just below, the lower edge of the windows) -- would be one color and the rest of the car another.
As noted, in the mid-1950s this convention had been abandoned and marketers were urging stylists to keep up with the competition by creating increasingly baroque color patterns. Unlike nowadays, most brands were based on a single "platform" or basic body. So stylists had what amounted to a single canvas to decorate using various color area patterns.
The present post features 1956 Fords. The Thunderbird and station wagons aside, Ford offered three lines: the entry-level Mainline, the intermediate Customline and the top-level Fairlane. Each had its side color/trim design.