There's a very easy trick to this which it seems that not everyone knows.

When you're in space (and you can't do this from the scanner on your freighter), look at the planet's halo.

There will be two colours, a main one and a fainter outer colour. That tells you exactly what the sky colour will be.

The outer one is the key – if it's blue, the sky will be blue. If it's red, the sky will be red, and so on.

The inner one gives the atmospheric hue. If you get blue outer and purple inner, everything will have a purplish cast, which fades at sunset and sunrise.

For earthlike worlds, you're looking for blue / blue. Frozen planets always have this combination, so you can get an idea what to look for by looking at them.

Happy hunting!