The base of the insulator is the same color, burnt honey brown all the way down to the bottom.
Why wouldn't you use both plugs for ignition on the new head?
If it is not jet black or blistered white, you are in a workable range. Need new plugs to fine tune jetting.
You know I mean the insulator inside the engine, inside the threaded shell?
I think you know this, but where you include a picture of the exterior plug insulator I thought I'd make it clear.
You could fire both plugs, it makes little difference.
I had a 1974 CR250 Elsinore many years ago that would foul plugs constantly because:
1) I used crappy oil,
2) I used crappy plugs
3) I jetted too rich (cuz more is better, right?)
4) I used too much crappy oil (cuz more is better, right?)
5) too much low speed trail riding
My answer, like most of us, was to MODIFY!
I stuck on a twin plug MT250 head with a cold plug for running hard and a hot plug for trails.
Didn't work. Hot plug runs hot even if no wire to it and when one fouls, they both foul.
Try out your ideas. Even when they don't work you can learn something.
Steve