RAF and FAA camouflage patterns and colours were developed by the RAE in the 1930s. The A and B patterns were mirror images of each other and were to be applied to alternate airframes. A natural consequence of this is, depending upon the serial number of the first aircraft and which pattern chosen to be applied first, is that the even and odd serial numbers will have the same pattern, A or B, applied. There are some people who think whatever they see on Spitfires is somehow universal and think that the A pattern was applied to aircraft with even serial numbers and the B pattern to aircraft with odd serial numbers. That is not the case. Generally Spitfires with even serial numbers had the A pattern applied while odd serial numbers had the B pattern applied. With Hurricanes it is the opposite, odd serials have the A pattern and even serials the B pattern. There are, as is usually the case, exceptions to the rule.

There is some evidence that originally four patterns were envisaged, the other two presumably being the A and B patterns with the colours transposed. At least one Fairey Battle in France is known to have had one of these transposed patterns.

In January 1941 the A and B pattern system was abandoned and manufacturers were told to choose either the A or B pattern and apply that to all aircraft. Most seem to have chosen the A pattern.