From left to right it symbolises the RN, The Army and the RAF. In seniority. The design in the centre has symbols from all 3 services.
It must have been a Tri service establishment. Where and what exactly?
Just my observation, but the RAF seem very keen on purple-ization, but only as long as they get to keep there slack ways and get to wear what they denigrate as 'cabbage kit' or CS95s, in camp/shore establishment.
It used to make me laugh at Blandford when RSM made them change into their crabfat blues to use the mess for meals. Half of them would rather get a pastie from the museum cafe instead.