Since the atmosphere is made up of oxygen and nitrogen, which are much smaller than the wavelength of light, they scatter all light with a blue wavelength. In Mie scattering, a larger particle, such as a cloud drop, would scatter all light. This is why clouds are white. Well, they are the effect of light refracting off of a raindrops. It is exactly the same way a prism works.
White light enters a raindrop, and is refracted off the back edge of the raindrop.
Light of different colors is refracted by different amounts, which makes the spectrum of colors. Blue light is bent more than red light because the index of refraction increases as the wavelength of light decreses. And these are only a few examples of what can be explained by radiation.