Civilian M20/21colours
1937 The M20/21 model had a finish of black for the frame, forks, headlamp shell, mudguards, oil tank, toolbox, chain case and chain guard. The exhaust system, headlamp rim, handlebars and some minor parts were chrome plated. Green tanks with gold lining and oval tank transfer, option of chrome plated tank with green panels, black rims.
1938 As 1937, except for chrome plated rims with black centres.
1939 M20/21 Standard: chrome plated tanks with matt silver panels, round BSA tanks badge, black rims. M20/21 de-Luxe: chrome plated tanks with matt silver panels, round BSA tanks badge, chrome plated rims with matt silver centres.
1940 Matt silver tank with black outer and red inner lining, BSA oval badges.
1945 The M20 model had a finish of black for the frame, forks, headlamp shell, mudguards, oil tank, toolbox, chain case and chain guard. The exhaust system, headlamp rim, handlebars and some minor parts were chrome plated. Matt silver tank lined in black, black rims and brake back plates.
1946 As 1945. Also M21 again.
1947 As 1946.
1948 As 1947, M20/21 options:  Telescopic front fork, chrome plated tank with matt silver panels lined in black, rims chrome plated with matt silver centres lined black. Black brake back plates. 
1949 As in 1948 with same options.
1950 As in 1949.
1951 No changes but during the year the nickel supply position bagan to restrict chrome plating. Plunger rear suspension as option. 
1952 No changes were announced but during the year nickel was in short supply so tanks and wheel rims were painted. Chrome plating was restricted to the exhaust pipes, silencers and minor fittings. Tanks carried small round BSA badges with a wing pattern.
1953 Maroon tank with chrome side panels, all other parts in black. Chrome plated wheel rims.
1954 As 1953 with maroon tank and large plastic tank badges, remainder in black.
1955 As 1954, last year for M20.
1956 As 1954, Just M21.
1957 As 1954, but with cream tanks panels as standard, chrome plated panels as option. Just M21.
1958 As 1957, Just M21.
1959 As 1957, Just M21.
1960 As 1957, Just M21.
1961 As 1959, Just M21.
1962 As 1961, Just M21.