There are a few ways to go about disproving a literary theory. For instance if the story was written before Star Trek was a thing. You could look for whether red has a stronger connection to something else, or if it's colors in general.    Just make a stronger argument. "It's coincidence" is basically the null hypothesis and it doesn't make for great discussion because you can assume that about any claim, but it can still be accurate. You just need to have an argument for *why* you think it's coincidence. You put in the work to show exactly how the evidence provided is flimsy or the connection weak.    >it's really hard to prove them wrong, even if they don't have any evidence or compelling reason.     If the argument and evidence is really that weak it shouldn't be all that difficult to demonstrate it. Tell them *why* the evidence is weak. Is the color Red used elsewhere besides shirts? Was the story written before Star Trek was a thing, etc.     Part of literary analysis is being able to articulate arguments against other theories and supposing your own.