At our institution we have 3 levels:
1. Scope positive-maybe, maybe not.
2. TV positive-the monitor in the multi-head room makes brown things look browner, so if we want something to be positive that's questionable on the scope, we look at the TV and see if it's "TV positive"
3. Fed Ex positive-if the Fed Ex man (or woman) delivering outside slides can look at them and say, "Yup, looks brown to me", it's Fed Ex positive.
Hope that helps.