Up until the 1940s, color television relied on a mechanical scanning system that used three monochrome colors to produce a color broadcast or transmission. John Logie Baird, who had previously demonstrated a system that juxtaposing a black-and-white display with a rotating colored filter, started working on a superior, fully electronic system around 1940. After Baird's premature death later that decade, other companies developed systems similar to Baird's "Telechrome" technology. RCA engineers achieved the one on the left. Unlike mechanical systems, which used a rotating disk to transmit three colors at one time, this system split a single beam of light into red, blue, and green images. Three kinescopes containing the cathode ray, projection, and tubes would simultaneously pick up and project the merged color picture onto the screen.
Read the full story in Electronic Color Television is Here