In the past , `` Orange Street '' was a connection between the city and the rest of the continent .
The Orange Line is so named because it used to run along Orange Street ( now lower Washington Street ) ; the Green Line because it runs adjacent to parts of the Emerald Necklace park system ; the Blue Line because it runs under Boston Harbor ; and the Red Line because its northernmost station used to be at Harvard University , whose school color is crimson .
Massachusetts Bay Transportation Authority