Throttle Lever Colours
This may not answer the question fully but, as a member of the team preserving XM496 at Kemble, my answer when asked by visitors why the throttles are topped with different colours, is usually that red for port and green for starboard would be logical but red levers and red lights on a flight deck are often for emergency use or are warning indications so the manufacturer presumably chose yellow for numbers 1 and 2 as a safer alternative. I may be wrong, in fact as Britannia aircrew from 50 plus years ago, I can't remember for certain what colours the levers were originally and the manuals are all in black and white!