Red was added to the Golden Arches logo in the 1960s to create its familiar red-and-yellow version. The bright combination made the mark highly visible on signs, buildings, packaging, and advertising.
The yellow arches themselves came from McDonald’s restaurant architecture and were later simplified into the M-shaped corporate symbol. Adding red gave the logo a strong contrasting field and helped establish a consistent visual system.
McDonald’s has used variations of the arches in different eras and markets, including versions with a green background or a single-color treatment. Those variants do not change the historical importance of the classic red-and-yellow combination.
The answer is sometimes confused with green because contemporary restaurants in some countries use green backgrounds as part of a more environmentally styled appearance. Green is a later design variation, not the classic color added in the 1960s.