There are some great explanations here of why we see a blue sky on Earth, eg here.

Namely: a combination of (a) the mix of colours from the Sun (eg, more green than indigo), plus (b) Rayleigh scattering from gas molecules (preferentially scattering shorter wavelengths, ie indigo/blue) plus (c) the sensitivity of our eyes (we see green better than indigo).

And, that when Sun is low and light going through ~2000km of atmosphere rather than ~10km, Rayleigh scattering means very little blue light left, so the end effect is a reddish sky. (I'll admit that one has always confused me: a bit of scattering = blue, but a lot of scattering = NOT blue...this looks a good explanation tho)

My question is why is sky red on Mars.

I've seen two explanations, both dependent on the fact that the much thinner atmosphere means the effect of Rayleigh scattering of light by gas is dominated by the effect of airborne dust.

Explanation one: the airborne dust scatters out all the blue light, so that the sky we'd see is reddish for same reason our sunrise/sunset sky is reddish. (Because there's so much dust?)

Or, simply that because the dust is red (because the surface of Mars is red - lots of iron oxide), we would see a reddish sky.

Can anyone help with this?