It is my understanding that Rayleigh scattering depends on both the length of the particle as well as the wavelength. Due to the similar lengths of molecular nitrogen and oxygen it is blue light that gets scattered down to Earth giving the terrestrial sky its blue color. But what about Titan? The Titanian atmosphere has a vastly different chemical composition than Earth(on Titan it is mostly nitrogen dioxide and methane). So is there evidence that Nitrogen Dioxide and Methane tend to scatter longer wavelengths than molecular nitrogen and oxygen do? Hence why extraterrestrial skies are not always blue like Earths.