The heat makes them change color down the plug. I'm also not sure how much of the plug sticks into the top of the chamber, but, as you can tell, there's a LOT of threading on it. Mine matches 2(1) Normal - which of course makes me happy, especially after the abuse they've went through, including judicious use of @COBB Tuning's 93 tune.Interesting. I understand it on the sparky side facing the combustion chamber, but the threads are what stuck out to me. When tightly sealed I wouldn’t think they’d change color that much. In comparison I pulled plugs from my 98 Bimmer with 231k mi on it and the end looked a little more grey but the threads were clean. No idea how many miles are on those plugs.