This request is rather interesting. The word "Безмирно" doesn't exist in Russian, but the author of this lines is the famous writer, so he has the right to create new words I guess.
I read a few examples of using this word by author and I think "Безмирно-Ñинее" means the following:
- Blue without the shades that this world casts to it, blue that is not merged with the colours of this world (smoke, reflections, nature, weather). Blue as it is, not as people see or imagine it. Literally - wordless blue.
So, may be genuine blue can fit if there isn't more beautiful word combination or phrase.
- Restless is unlikely to be the meaning, though no one can say for sure. The second literal translation possible is peaceless.