I'd be sending that photo to Metzeler pal

Lets face it, if it's nowt serious then carry on as normal

But if it's something they've not seen before, it could be important

I'm obviously no "tyre technician" but I've not seen that effect before

On ANY tyre over the last 50 odd years

It does look as if there may be more than one compound or maybe what we see is the "edge" of a layer

Either way I'm sure "peace of mind" is what you want

So send a few pics to the technical bods at Metzeler and see what they say

Keep us posted with your "investigations" bro