Bonjour rvictor!
In respect of the concerns that you have regarding Nieuport 17 B1556 when flown by
Billy Bishop -
I believe that the border of the serial B1556 on the rudder was white and blue with the colour, obviously, on the white portion only.
The aircraft was in essence coloured silver.
With the assumption that standard practice was followed British roundels would have been applied to the upper and lower surface of the upper wing and the lower surface of the lower wing and the sides of the fuselage.
C and 5 were applied to the port side and starboard side of the fuselage either side of the roundel ... note that the C was before the roundel on both sides.
As to the issues of concern -
C and 5 may may or may not have been applied to the upper surface of the fuselage ... there does not appear to be absolute confirmation, but, it is assumed by many that the designation was to be found behind the cockpit at some point in time.
C appeared on the starboard wing between the roundel and the fuselage and 5 appeared on the port wing between the fuselage and the roundel.
The cowling over the engine and the wheel covers were painted "Royal Blue" (to quote Bishop).
The armament of the aircraft was a single Lewis gun mounted over the upper wing.
Note as well that the aircraft sported a maple leaf painted on the port side, approximately 12 inches from top to bottom, in autumn colours.
At some time a doll was mounted to the bottom of the starboard struts between the wings.
The majority of the information listed can be found in the article Bishop's Aircraft - Colours And Markings No. 60 Squadron, RFC by the late Philip Markham and Greg Van Wyngarden which appeared in Over The Front, Volume 10, Number 3, Fall 1995.
Salut!
Kirk