Dan,
Night Enforcer has some very good ideas. The plugs will vary in color, gas on them and etc, depending on how they have been driven and what type of gas you use plus any additives. The # 7 plug is the only one that looks a little odd to me and the could be the flash. The way I used to check mine was put in a new set, run them for a while and then make a hard run and shut the motor off just as NASCAR does. Then pull the plugs and check them. Also because of our lousy gas, I changed mine more often than most people.
Ron
