Why are my plugs all different colours?

[Skidmarx]

id like to know what some people think the advantages are of using a higher octane fuel on an internal combustion engine that has not been tuned to gain anything from it, i run my gen1 on united 95 ethanol blend, coz its cheap, doesnt run any better or worse, infact iv found i can run a tad more timing, running the blended fuel over any of the top brand 98's around

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and yes my findings have all been on dyno with logging of afr's and such