Daytime sky color is a perception, not a pigment. Sunlight enters the atmosphere as a spectrum, carrying a continuous range of wavelengths from violet through red. Gas molecules and tiny particles act as scattering centers, redirecting incoming light in many directions. This process, known as Rayleigh scattering, acts much more strongly on shorter wavelengths, especially those in the blue and violet region of the visible spectrum.
Because scattering intensity scales with the inverse fourth power of wavelength, blue photons are redirected far more efficiently than red ones, a textbook case of a steep marginal effect in physics. The human eye, with cone sensitivity peaking in the blue-green, converts this biased stream of scattered light into the impression of a blue dome. The phenomenon also increases optical entropy in the system, redistributing ordered sunlight into a diffuse field. The sky is not full of blue; it is full of scattered white light, selectively filtered by atmospheric physics and finally edited by human vision.
As the viewing angle shifts toward the Sun, the path through air shortens, direct light overwhelms the scattered component, and the sky washes toward white. Near the horizon, a longer atmospheric path preferentially removes blue from the direct beam, leaving transmitted light richer in red and orange, while the overhead vault remains dominated by blue scatter. A color that seems painted across the heavens is, in practice, an emergent compromise between radiative transfer in air and the biology of sight.
