For comparison, this is the standard version that you see plenty of nowadays:

A few different versions with different shades of blue and yellow circulate. I have not really managed to pinpoint which versions where used where and when. Any opinions on which color combination works best?

It is a bit curious that Russia also darkened the blue on their flags and changed the proportions to 2:3 after independence. As far as I know, it’s just a coincidence.

The flag matches a typical Ukranian wheat field, leading to some of the nicest “photorealistic” flags:

blue sky over yellow wheat field

Although this is nice symbolism, it’s likely not the origin of the flag. Already in 1410 Lwów/Lviv used a blue-yellow banner, which could be the origin of the colors:

banner with yellow lion on blue

Wikipedia article about the flag