I used to live a couple of doors away from an active coal-yard. Not so good when you have two black and white cats.....
The number of times they came home black and grey cats. . . . . .
Lucky would always have a good wash.
Gizmo (Bless him) had more white so maybe he thought it wasnt worth it.
He would sat in the middle of my white, bedside sheepskin rug and then roll ..... Result? Grey rug - clean cat