My cat Gator is a good 9+ years old now, He has what I call "Black Patches" (A tad lighter then the actual color black) The pictures below is the back of his feet... He also has this what I call "Black Patch" on one of his front paws.. I know he's not in pain, but iv'e always been curious to what it is... When he was younger he did have a stroke and both of his back legs were paralyzed until I gave him some Omega 3 Fish Oil, He came back to life.. We also brought him to the vet, But it was so long ago that I don't remember if they diagnose the problem or not, but I'm hoping that its nothing serious.