Black dust on my rear bumper

[WhipE350]

I get this also. Car is Guards Red so it doesn't show too bad. Carry a microfiber towel and just keep it clean. It is dust, rubber from other cars on the road, and from your tires. I have checked it after different types of very short and long trips. It is always worse after I drive hard...likely because I'm throwing up more crud from the road and because I'm slinging my on rubber.