You are correct. The silver ones are made in France and the others are made in Japan. I thought they were counterfeit at first but according to the NGK website they appear to be Ok. Iridium already fitted just have to check the mixture with the colour tune.
When setting the mixtures with a Colortune Plug, I would advise you give the bike a good run first (min 10 miles or so) before you do so, to ensure its all at correct running temp and the valves and seats are as clean as possible.
Its not a good idea to start from cold at low revs and warm it up on tick-over then check as you can find different readings from both.
Also if you have fitted new O Rings to the mixture screws, then ensure they have a thin coating of grease on them and screw them IN and OUT a few times before setting them to ensure they are fully seating before counting the turns OUT.........as the new O Rings will be tight and can give a false seating feel.
I continue to use silicone "square" seals on my Pilot-needles. Have been installing them on "rebuilds" for several years now. Have a "stacked" cutter that produces 6 at a time from small dia. glow engine fuel tubing and personally don't see myself ever going back to the OEM style O-ring. They seal with far better effectiveness, give a nice feel of resistance and on my own bike - have removed the springs that gouge material from the pilot-needle. And again I'll beat the bushes by promoting the modification to the head of the pilot-needles with a small socket head that completely eliminates the "pissing-'round" associated with a slotted driver. Remove and re-install and adjusted accurately with a magnetized ball-end driver.
1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !