old lancashire saying

[janetiqua]

Where does the phrase "as black as up lovers" come from. Suggestions have been a mining term, or simply as dark as lovers lane. Any one any thoughts or facts.
Serious answers would be appreciated, as it was a phrase my mother used now sadly not around to ask

[Cleggy]

My grandfather, also a miner, used to say "It's black over Bill's mothers' " Meaning over there