Funny, that cylinder monitoring thing was called "Colortune". I have one. It
consisted of a spark plug with clear glass insulator which conducted the
light of combustion out of the cylinder. An a small mirror to see it better.
Not surprisingly, it is not ver much different than the flame color in a gas
furnace. Blue-white is lean and yellow orange is rich.
The only practical use of such a thing is to set the mixture at idle. It
would be pretty diffficult to put one's face down by the spark plug while
the engine was under full load.
(Well, it was the 60's and it WAS made in Britain!) But still kinda neat.
Al Brase