I have to believe that there are several US Navy coffee messes haze gray and under way that could give this product a run for its money. Is it more about the variety of beans or the residue in a well seasoned coffee pot? I never wash my coffee cup, the day may come when there is no coffee just hot water. Having a good build up of coffee residue can come in handy! The down side? You will need to buy a new cup - when the hole grows shut (10-12 years on average so account for that in your annual budget).
I can explain it to you but I can't understand it for you.
"Any man who thinks he can be happy and prosperous by letting the Government take care of him; better take a closer look at the American Indian." - Henry Ford
Corruptissima re publica plurimae leges; When the Republic is at its most corrupt the laws are most numerous. - Publius Cornelius Tacitus