Color Tune

[Hans Hintermaier]

John Dammeyer wrote:
<I have a color tune spark plug and I can use it to set
<idle mixture by looking through the quartz window in the sparkplug and
<adjusting for blue ignition;  too rich is yellow/orange

Can anybody tell me something about the colortune spark plug ?
(manufactor, price) I know it only as glow plug for model engines and 
have never heared about spark plugs with the same feature.
Thanks
Hans
hiha@ brain.nefo.med.uni-muenchen.de
Munich / Germany