Spitfire mk i squadron code colour

Hi. I've noticed vastly different shades of gray used for spitfire mk i squadron code decals (in the period May-September 1940). The shades vary from light gray to very dark gray.

Was there any variation at squadron level of the shade of grey used to paint the squadron lettering (ie different batches of paint) or was it one standard colour?

Thanks in advance!

Official Documents:
A.154 (27.4.39)
5. The code letters allotted to squadrons are shown at the appendix to this order. They are to be painted in grey paint {Stores Ref. 33B/157). The letters are to be 48 in. high and are to be made up of strokes 6 in. in width. Smaller letters are to be used only when the space available on the fuselage makes such a course unavoidable.
AMO A.926/40 (12.12.40)
(vi) Code Letters.---Code Letters are carried by service types in operational units and operational training units. The two code letters and one letter to indicate individual aircraft are to be painted in grey paint and placed before and behind the roundels on the fuselage. The code and individual letters may be placed two before and one behind the roundels or vice versa. The letters are to be 48 in. high and are to be made up of strokes 6 in. in width. Smaller letters are to be used only when the space available on the fuselage makes such a course unavoidable.
This covers your time frame. As is known, paints from the manufacturers vary in shade

Thanks fubar57, this is most helpful.

I will thus explain the different colours of gray as being from diffetent paint suppliers!