ippytattoo
Just another grumpy old hack.
Yes it is probably just a coincidence they look that way. A quick measurement of the friction plates will verify the thickness and a magnet will tell you if it is steel or alloy. A quick way to see what is under the black on your others is to take a small flat hand file and "clean up" between a couple fingers on one of your friction plates and you will see the same metal underneath. If you just clean off some of the black it will not affect the performance of the clutch.