At one time we had a set of cups that were brown. My new bride would sometimes make gravy with the packets of powdered stuff, some of that stuff is onions. She would dump the stuff from the packet into a cup, add boiling water, stir, for instant gravy. Whomever washed the dishes one time did not get all the gunk out of the bottom of the cup. A few days latter a new friend came by for a visit. As is the custom in most homes he was offered a cup of Joe, guess what cup he got. He never said anything until about five years later when he knew our friendship could handle knowing the story. He said that he just thought that we maybe like onions in everything, but we never served him that kind of coffee again, but he always checked his cup prior to our filling it. A few years later he was working for a hunting guide up in the Yukon Flats, his job was as a packer, skinner, all around camp helper and cooks helper. As luck would have it at my job one day I saw the head guide in the Alaska Dept. of Fish & Game with three new clients getting their hunting license and tags. I told them the story about Ron and the onion tasting coffee. They readily agreed to after a few days in camp to one morning all look up at Ron after their first sips of morning coffee and asked "who put onions in the coffee?" Ron didn't know that I had met these men, so it was a good joke. We have since then, gotten a set of white china, the white cups get inspected very carefully prior to use.
I have bunked in many old run down mouse, vole, and squirrel infested trappers shacks and fish camps, I always turn the pots, pans, bowls, and cups upside down and give them a good rap to make sure that no feces would be floating in the brew.