While working in various RAF calibration labs in the sixties and early seventies I used to clean and calibrate watches as well as doing the usual aircraft general instrument work. I remember the Hamilton GS as the most common, at least on the 'V' force with the Smiths W10 a close second. IWC XIs were common on transport command and I saw the occasional CWC and Omega chronographs, but navigators were famously reluctant to surrender these to the stores for routine servicing. They took them to the local jewellers generally. I wonder why?
Of the first three common watches above, I found the Hamilton GS's to be the most accurate with differences between face-up, pendant up and pendant down measurements of less than a second in 48 hours. Not bad for an old clunker. The Rolex Chronograph Daytona that I bought for myself in Singapore wasn't a patch on the Hamilton for accuracy or reliability. I've used a Seiko Premier ever since - probably the best watch on the market [but much too small for pilots
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I believe the British government are buying a military version of this watch for general issue at the moment..
On the question of colour, I've never seen an RAF issue watch that wasn't white or luminous green hands/figures on a black background. That doesn't mean that there weren't any others, but it does suggest that the specification called for those colours.