I"ve heard northerns can be a brown or grey and on occasion there has even been black ones found. I don't know if it was a northern but a couple years ago I found a sweet little dark one that looked near black. Beautiful snakes!! They don't do well in captivity though and usually wont eat well. I think they eat slugs mostly in the wild.
Herps are like pringles, you can't stop at just one.
'believe me I know!!'