Carbon on inside of tailpipe

I have a 2014 500L, with the 1.4 turbo. It has 18k miles on It now. Fuel consomption,, and performance good. Since new, it has always had black carbon inside of exhaust tip/tailpipe. My driving is a lot of highway, little city, and car has no periods of long idleing. I do not warm vehicle up, but drive off easy. Studio says air fuel ratio in specs. I feel it's running rich.

Can any of you with turbo, comment on appearance of inside of you exhaust?

Any comments appreciated.

Vin_ams