What would the air on a planet look like if it had a mostly methane atmosphere?

This is an edit of a previous question. It has been edited so I can be more specific in my asking, as I'm still confused after looking at the answers to a similar question to my original. I have a very specific situation in mind, and I don't want to get something wrong that would make anyone with an atmospheric science background immediately cringe. Small market, I know, but it's important to me to be correct in this case. I'm looking to get as accurate an answer as I can, so I've added the "hard science" tag to this version:

A planet orbits a blue giant in a non-tidally-locked fashion. The planet itself has an average temperature just above freezing, and radius of 3000-ish km. The atmosphere is ~75% methane, is otherwise mostly water vapor/CO2, and only slightly less dense than Earth's. I'm imagining it as being dusty enough to resemble a blue-hued version of Titan when standing on its surface, with a high density of cobalt giving the dust a blue color. Does the sky appear blue in the sunset, or does Rayleigh scattering still make it look red? I'd imagine that the planet would look fairly blue looking down at it, and everything about it screams "deep blue sky", but I'm curious if there's something I'm not thinking of that would make the sky look anything other than blue.

posted almost 8 years ago

Viddog‭

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