Final answer:
Tennis balls are yellow-green because this color is highly visible and easily tracked by our eyes, which are particularly sensitive to this range of the light spectrum, aiding both players and spectators in following the game.
Step-by-step explanation:
The reason tennis balls are yellow-green is primarily because our eyes are most sensitive to that color. This sensitivity makes them more visible on the court, facilitating better ball tracking during matches. The yellow-green color of tennis balls falls within the range of wavelengths our eyes can detect very effectively.
Human color perception is quite complex and although it's tied to the wavelengths of visible light, it involves the brain's interpretation of signals from the eyes' cones. Humans generally have three types of cones that are sensitive to different ranges of wavelengths corresponding to red, green, and blue.
In the context of tennis, choosing a yellow-green color maximizes visibility under various lighting conditions, which is essential during fast-paced games. This is not so much about tradition but about the practicality of ensuring that both players and spectators can follow the game with ease. In essence, the yellow-green color aids in maintaining color constancy in variable lighting, something our eye-brain color-sensing system is adept at.