Green

In the visible light spectrum, green occupies a wavelength range of roughly 495 to 570 nanometers. It sits comfortably between the shorter wavelengths of blue light and the longer wavelengths of yellow light.

Green is intrinsically associated with nature, vegetation, and ecological health, which led to its adoption as the primary symbol for environmentalism. Organizations like the Green Party and Greenpeace specifically use the color to represent their focus on sustainability and planetary conservation.

Standardized by railroad conventions in the early 20th century, green was eventually chosen to indicate 'go' largely for its high visibility and clear contrast against red. The specific shade of traffic-light green often includes a hint of blue to make it highly distinguishable for individuals with red-green color blindness.

Human eyes have three types of cone cells for processing color vision, and the cells most sensitive to green light (M cones) are the most numerous. Because our sun emits a peak concentration of light in the green spectrum, human evolution heavily favored the ability to discern different shades of green in forested environments.