Color processes using only two primary hues instead of three — Technicolor, early trichrom methods. Restricted gamut but significantly better than black-and-white.
Before the Technicolor three-strip process, an entire era of color film was dominated by two-color systems. These systems reduced chromatic information to two primary colors—usually red and green, or red and cyan. This sounds like a compromise, but it was technically elegant and revolutionary for its time. Instead of three separate film strips, only two color-sensitive layers or two exposed negatives were needed, which were later combined. This reduced costs, camera equipment weight, and laboratory complexity. Practitioners knew back then: you weren't working with a full color spectrum, but consciously orchestrating a limited palette.
The early Technicolor Two-Color (from 1916) and later Technicolor Process 2 (1922–1950s) simultaneously show the limitations and strengths. Blues were difficult to render—the sky in two-color systems was often artificially colored or appeared greenish. Skin tones tended toward orange-red, and vegetation toward unnatural magenta. Nevertheless, on screen, these films didn't look unsatisfactory but rather characterful. The cinematographer had to consciously adjust lighting to optimally utilize the available two channels. Costumes and set design were planned with this color limitation in mind—it wasn't a bug, but an aesthetic rule of play.
Historically replaced by the three-strip Technicolor from the 1930s onward, which fully separated red, green, and blue. But two-color systems shaped the visual grammar of an entire decade of film. Modern colorization of old black-and-white footage or the deliberate simulation of two-color aesthetics in retro productions requires an understanding of these limitations—not as errors, but as design principles. Today, it's interesting for color correction and VFX archival work when combining historical sequences with modern material. You need to know how the old palette functions to authentically emulate it or to break it in a controlled manner.