Rayleigh scattering is strongest for wavelengths much smaller than the scatterer, scaling as 1/λ⁴: blue light at 450 nm is scattered ≈4.4× more strongly than deep red at 650 nm. Look anywhere but at the Sun and you see that scattered light — blue-rich. (The sky isn't violet because the Sun emits less violet and our eyes are barely sensitive to it.) Near the horizon the light has crossed more air and re-scattered, washing the blue toward white.

At sunset the beam crosses up to ~38× more atmosphere: the blues are scattered away long before the light reaches you, so the direct beam arrives red-orange and paints the clouds. Clouds are white because their droplets are much larger than any wavelength (Mie scattering — all colours equally). On Mars the thin dusty air does the opposite: butterscotch sky by day, blue glow around the setting Sun. And on the Moon, with no atmosphere at all, the "sky" is black even at noon.