Why does the Sun, whose peak emission is green, appear white or yellow-white to human perception?

Because the star emits light across all visible colors simultaneously, and the eye blends these multiple emissions together into white or yellow-white light.

Although the Sun's peak energy output falls precisely in the green region of the spectrum due to its 5,800 K surface temperature, this value represents only the single wavelength of greatest intensity, not the total light being emitted. Stars emit a continuous spectrum covering all visible wavelengths—blue, green, yellow, and red. When the output intensity across this continuous range is significant, particularly when the green peak is flanked by strong blue and red emissions, the human visual system integrates all these inputs. This integration leads to the composite perception of white or yellow-white light, preventing the central green peak from being distinctly perceived on its own.