The resultant color of the finger(s) of a person who has just wiped their posterior after defacating, except they didn't wash their hands with soap and water before leaving the bathroom. Related to "yellow finger", a person who does not wash their hands with soap and water after urinating. A person who lives in Oregon and pees outside is not considered a yellow finger if they do not wash up after urinating since their are no sinks handy and a real man does not pee all over his hand no mater where he pees. An office worker who doesn't wash up is always a yellow finger.
"Man, did you know Joe is a brown finger? Dude didn't wash his hands after wiping his posterior after defacating"
"Damn, Steve is a yellow finger and a brown finger."
"Damn, Paul needs to go see his gastroenterologist. The freak ruined the flowery smell in the bathroom with his incessant farting and fails to wash his brown fingers post defacation."