More black stuff on the front wheels is perfectly normal, because something like 60% of the vehicles' braking is done by the front brakes.
If you want to reduce the black appearance significantly, get a set of ceramic brake pads and dump what you have now or sell it to someone who doesn;t have an issue with brake dust.
OE pads in particular are soft and leave lots of dark powder on the front wheels. Switching to PBR deluxe pads reduces the effect somewhat, but ceramic pads are the way to go.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!