Were it not for this scatter, on a clear day the sky would look black every where except when you looked directly at the sun. (DON’T EVER.) However, clusters of water molecules from 0.3 to 100 nm suspended in the atmosphere are the right size to scatter photons. Therefore rays of sunlight original headed elsewhere will have some of their photons scattered in your direction. Since more short wavelength photons are scattered, they predominate. Their blue sensory effect is attributed to the sky in the direction from which they arrived.
The water droplets that make up clouds are several orders of magnitude larger. Therefore clouds are Lambertian, reflect all wavelengths equally, and appear white. A continuous range of particle sizes from single atoms of water to rain drops provide a range of effects depending on conditions.