I can definitively state that Lucas did, in fact, make amber L549 tail lenses. As far as I can tell, they were made from late 1954 through early 1957, and XK140s and Mark VIIM and VIII cars sometimes were fitted with these. My own 140 FHC has them, as does a Mark VIII parts car we have here. An old friend purchased his MGA roadster in New York in 1956, and it came with amber L549 lenses, which is still wears today, and I spoke with a fellow who bought a TR3 new in 1956 which came with amber rears.
Rogers Motors specializes in selling obscure Lucas parts for old British cars, and we have purchased a few of these amber lenses in the UK over the years. We have a few on the shelf at the moment, at the risk of sounding like a commercial announcement… one pair is NOS from a Mark VIIM or Mark VIII, the other a used set from an MGA or TR or similar; same lens, different base assembly.
As to amber or clear front flasher lamps (L563), XKs, big saloons and Mark 2s were fitted with amber lenses in pretty much all markets apart from the US (not sure about Canada) because US regs forbade amber front lamps in the fifties and sixties, Similarly, headlamps with bulbs were also forbidden in the US during that same time, and since Lucas did not make sealed beams until late 1959, all British cars exported to the US came with black plastic discs in place of headlamps, while the dealers fitted locally-sourced sealed beams, made by TS, Westinghouse, GE, or whatever they wanted to buy.
The two-piece rear lamps used on late Mark IX and XK150 and Mark 2s (Lucas L627; same lens but different bases for each of those Jaguar models) had upper (flasher) lenses of amber in all markets except the US, which had red upper lenses.
Fog lights were also not used in Mark 2s because they were mounted too low to meet US specs.
We have amber tops and amber front flashers in our own ’63 3.8 MK 2 because we like them that way, as they go very well with dark green, but the car came with clear fronts and red rears.
It’s an irony that in the US today, all new cars have bulbs in the headlamps, amber flashing lights and many have factory fog lights, mounted way down low!