The sky looks blue due to

Explanation

Blue colour of the sky is due to scattering of sunlight by air molecules. According to Reyleigh.s law, intensity of scattered light. `I prop (1)/(lambda^(4))`. So blue light of shorter wavelenght is scatterted much more than red light of larger wavelenght. The blue component is proportionally more in light coming from different parts of the sky. That is why the sky appear blue.
Clouds have large particles like dust and water droples which scatter lighe of all colours almost equally. Hence clouds generally appear white.