The trigger guard is "nitre blue." I think that may be noted somewhere in Brophy. The higher grade guns that I have (which have what I believe to be original finish, including a Speciality Grade), all have case-colored forend iron. I do have a Field Grade, NIB from 1925, that has blued forend iron; I can't tell for sure whether it is nitre blued or not, but I'm inclined to think it is.