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.
The blue sky on Earth is because of Rayleigh scattering, and because the particles in the air scatter blue light more then red.
This is the Tyndall effect, he discovered that when light passes through a fluid with particles in suspension, blue light is scattered more then red.
The amount of light scattered is inversely proportional to the fourth power of the wavelength.
This works if the particles are small. Much smaller then the wavelength.
The sky on titan is blue.
Please see here:
You are right, that the size of the particles in the atmosphere does decide the color of the sky, because with larger particles, Rayleigh scattering is not dominant, but Mie scattering is.
On Mars, Rayleigh scattering is usually a very weak effect; the red color of the sky is caused by the presence of iron(III) oxide in the airborne dust particles. These particles are larger in size than gas molecules, so most of the light is scattered by Mie scattering. Dust absorbs blue light and scatters longer wavelengths (red, orange, yellow).