Question

Why does the bluish colour predominate in a clear sky?

Answer 1

As the light from the sun travels through the atmosphere, it gets scattered in different direction by the air molecules present in its path. The blue(or violet) light due to its short wavelength is scattered more as compared to the red light of long wavelength. Thus light reaching our eye directly from the sun is rich in red colour while the light reaching our eye from all other direction of sun is the scattered blue light. Therefore the sky in direction other than the direction of sun is seen blue. 

Answer 2

Hey !!

At the time of sunrise or sunset, the sun is just above the horizon; sunlight travels a longer distance through the atmospheric particles. The amount of scattering is inversely proportional to the fourth power of the wavelength.

             I ∝ 1 / λ⁴

Since, λb << λr. Hence, the bluish colour predominates in the clear sky.

Good luck !!