Yep, Totally agree with TBM. That is a sign of a perfectly set up engine and all four plugs should look very similar. As engines wear, and nowadays we are talking starship mileages on well maintained engines, you will probably notice some difference to no. 1 and no. 4 plug and the same to the tops of the pistons. This doesn't mean you panic and expect an engine rebuild! Rather time to check the individual cylinder pressures and if they are within the acceptable range carry on!
