Amber, Red, Blue, Green numbered 1 to 3, 10 miles wide, 3000ft to 15000 ft.
The colours were they based on a quadrant idea? Presume the numbering was chronological. All roads led to LHR or atleast Epsom and Watford and onto the Kilburn intersection.
Occasionaly there was a Purple one but being pre Beecham rail was the prefered option.
"Going from NDB to NDB", routes coasted out over light houses because they had ndbs.
Then late '57? the upper limited increased to 30,000', started to call these upper levels FLs. There getting to be quite a lot of Viscounts about. April '58 introduced oneway systems and new airways with double digit numbers (blue23) for cross channel routes.
Hope the old brain cells have been reasonably accurate.