1-The colour of the sky is due to the property of dispersion of light the white light of the colour before reaching the earth's surface gets dispersed into its 7 components VIBGYOR the molecules present in the atmosphere are capable of scattering only the light with the shortest wavelength and hence red light won't get scattered2-The sky is blue not because the atmosphere absorbs the other colors, but because the atmosphere tends to scatter shorter wavelength (blue) light to a greater extent than longer wavelength (red) light. 3-Blue light from the sun is scattered every which way, much more so than the other colors, so when you look up at the daytime sky you see blue no matter where you look. 4-This scattering is called 'Rayleigh scattering'; the amount of scattering goes as the frequency of the light to the 4th power. 5-By the way, this effect is most prevalent when the particles that do the scattering are smaller than the wavelength of light, as is the case for the nitrogen and oxygen molecules in the atmosphere.