Ok, so the sky is blue because of Rayleigh scattering - blue wavelengths of light scatter off atmospheric particles in the air (more/more easily than others) - I understand this pretty well.
So, if our atmosphere had a different chemical composition, would the sky be a different color (barring things like clouds and dust)? I assume that the size of nitrogen molecules happens to be the perfect size to scatter blue light, so what if we had 78% helium instead, or hydrogen, or gaseous zinc?
If this is correct - which elements would need to be predominant in the atmosphere to produce red, orange, yellow, green, indigo and/or violet skies? If not, what am I misunderstanding about Rayleigh scattering?