Why is the sky a darker blue when you are at high altitudes?

The sky appears a darker blue at high altitudes due to the decreased amount of atmosphere above you. With less air to scatter sunlight, there are fewer air molecules and particles to diffuse the light, making the blue wavelengths more pronounced. This phenomenon is a result of Rayleigh scattering, which is more effective at shorter wavelengths, such as blue light. Consequently, the sky's color intensifies in clarity and depth at higher elevations.