This is an oft-quoted misconception; British Standards had no input with wartime colours, which were the exclusive province of Farnborough, under the auspices of the Air Ministry. ANA colours were the sole responsibility of the U.S., and were to their own standards.In 1940, Middle East Command requested a colour for their undersides (enclosing a sample,) and Farnborough were given the job of providing the mix, which they did. Azure Blue is actually quite a light shade, and it's believed that Humbrol's original colour was mistakenly matched to the post-war B.S. colour. Light Mediterranean Blue is also a completely separate (and darker) colour, which had no relationship to Azure Blue, whatsoever. In 1943, aircraft heading for the desert were ordered to have Azure Blue undersides, while those going through Malta were to have Light Mediterranean Blue.
The "nightmare" on Britmodeller is the result of genuine enthusiasts trying to make sense of a fiendishly difficult subject.
Edgar