Are you thinking 'dark and dirty' = unfair??
The closest 'unfair' would come to one of the meanings of 'murky' is "not fully explained or understood, especially through concealed dishonesty or immorality : "The murky world of espionage." It may not be fair is somebody is dishonest, but it doesn't make 'unfair' and 'murky' interchangeable.
Murky does not usually mean "unfair".
It is something that is complicated, probably unpleasant, and about which there is much that is unclear.
Have you a context for the word?