Different colored skies based on star's spectral type and atmospheric conditions

Okay, I'm writing a science-fiction story, and I'm trying to make it as realistic as possible, which means, the story is going to be plausible. Thus, I'm trying to figure out how to make an alien world be realistic. The planet is going to be Earth-like (to a certain extent), but there are going to be a lot of differences. For example, the star is not going to be a G main sequence star, and the planet isn't going to be the third planet, etc.

Here goes:
1) Star is a K0V star, meaning its mass is around .79 solar masses.
2) The planet is the fourth from the star, and lies approximately 0.562 AU, and has a mass of about 0.936 EM (Earth Mass). The star's HZ (habitable zone) is between 0.477 - 0.846 AU.
3) The planet has a nitrogen-oxygen atmosphere, just like Earth's atmosphere, but it also has much more argon and helium in its atmosphere than Earth does.
4) The planet is basically cold, with average surface temperature of between 4.4° C and 14.1° C (between 39.9° F and 57.4°F). It has very few clouds.
5) The planet has a large concentration of cobalt, since the lifeforms on the planet have indigo-colored blood, which is the result of their blood bimetallic hemoglobin, which is cobalt and iron (by the way, cobalt turns blue when it oxidizes).

Now, here's my question:
What would the planet's sky look like? What color would it have? I read in some books and articles that planets orbiting orange or red stars would have a green or greenish-blue sky. However, I'm not sure if this is correct (the book was a Star Trek roleplaying game book a friend loaned me a while back, and we all know how 'realistic' Star Trek is). Does anyone mind helping me out, please?

In addition, this topic can be used to figure out what other worlds' skies would look like as well.
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 Tags alien, atmosphere, extrasolar, sky, stars

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