For example, talking as if you think “simpler explanation” is a knockdown argument for evolution (which it is)
I don’t quite agree—by itself, X being “simpler” is a reason to increase my subjective belief that X is true (assuming that X is in a field where simplicity generally works) but it’s not enough to prove e.g. creationism false. Rather, it is the total lack of evidence for anything supernatural that is the knockdown argument—if I had reason to believe that even one instance of say, ghosts or the effects of prayer were true, then I’d have to think that creationism was possible as well.
Silas: red is not the set, but what all of those things have in common. The set would be most effective if you presented a sequence of examples that was different in every way except in color. To be extra sure of getting the point across, you could present examples that are exactly the same, except in color, and then say one was “red” and the other was “not red”—a whole educational philosophy has been built up out of this (look up Siegfried Engelmann and Direct Instruction). Of course this method of communication assumes that the audience is sighted, not colorblind, understands the concept of “same” and “different”, etc.