Rims Getting Stained

I noticed that 1 of my rims are getting stained and i believe it's coming from the brakes. I don't know if this is the right term "Brake Dust" but it's only happening on my front left rim. I tried cleaning it but the black stains won't come off, Is there anyone that has a solution to this problem. Has this happened to anyone else?

This normally happens if you don't clean them regularly. Or if there is a chip in your paint on the wheels allowing a crevas for brake dust to condemse and cake.