Because Blue light is scattered much more than other colours as it travels as shorter, smaller waves, we can ‘see’ these blue waves more clearly.
As we look towards the horizon, the blue colour tends to fade, often to white. This is because between our eyes and the horizon, all the different wavelengths of light are scattering so much that the colourful components of the visible spectrum appear to recombine to form WHITE LIGHT..
As many sky watchers, artists and photographers will be aware, we see many colours within most skies, especially when clouds are around!