blue boy
/ˈbluː bɔɪ/noun
1Any of various boys or men who wear blue clothing, or a blue uniform, livery, etc.; especially a boy who attends a blue coat school or similar charitable institution (now chiefly historical ).
2 Slang. A policeman. Also as a nickname. Usually in plural Compare boys in blue.
Origin
Mid 17th century; earliest use found in William Davenant (1606–1668), poet, playwright, and theatre manager. From blue + boy.