spark plug color or colour

[FGFO1@aol.com]

i may be way off base here and IM sure you all will tell me if i am.
back in the old country of leaded gas it was customary after a long run to 
check the color of the inside of the exhaust pipe. if it was a nice light brown 
you knew it was running right. now i never see that any more and i recall 
reading that unleaded does not give that indicator.
if all I have said is true would it not also apply to the old spark plug 
color guides too?
Frank Fisher
58 TR3A TS41366L
Temecula
California