The “Boys in Blue” are in blue thanks to Hainsworth. When the Air force separated from the Army in 1918 and approached Hainsworth for colour ideas to allow them to have their own identity, it was Hainsworth that proposed the distinctive blue cloth that they have worn ever since.
The RAF Blue colour has changed over time but the main colours for Royal Air Force uniforms are Wedgewood blue or blue-grey. Many air forces around the Commonwealth have adopted the same RAF Blue colours for their uniforms but naturally the flashes on their shoulders display their own nationality. The UK ATC and RAF (CCF) wear similar uniforms.