When I was a resident, our Pain clinic shared an office with GI Clinic (for some reason).
When patients came in, the nurses would put their charts out for us to see. The GI patients' charts were green and the Pain patients' charts were yellow.
So one day they ran out of yellow charts, I guess. So instead, they started putting out charts for the Spine patients that were orange-yellow. I came out from having seen a patient and I noticed that the other resident was just sitting there and had let like three charts stack up without seeing any of the patients. I pointed this out to him.
Resident: "Oh my god! Those were our patients?? But the charts aren't yellow!!"
Seriously, it wasn't that big a jump to figure out that the orange-yellow charts were ours. I mean, they clearly weren't green. They were basically just a shade darker. I figured it out somehow. I think some people are intentionally colorblind.
Anyway, a few days later, they ran out of the orange-yellow charts I guess, because they were putting out blue charts for us. I made a point out of telling the other resident that the blue charts were our patients, figuring that if a slightly darker shade of yellow threw him for a loop, he'd never be able to deduce that the blue charts were ours. (Despite the fact that we were the only people in clinic that morning.)