It's interesting in that people seem to trust meta-statements like the red label's more than they trust basic statements like the green label's.
That are the rules of puzzles.
> Portia explained to the suitor that of the three statements, at most one was true.
in a Gardner puzzle is evidence enough that we may trust that "of the three statements, at most one was true". Here, Portia is a character in the puzzle; why should we trust her any more than we should labels on boxes or (in the set-up of the puzzle) statements on caskets? If we have to distrust everything about the problem, then it seems to me that it runs into exactly the problem shultays (https://news.ycombinator.com/item?id=9837381) mentions.
(EDIT: I think that mdpopescu (https://news.ycombinator.com/item?id=9837257) said it better.)
Have you studied Descartes? "I think, therefore I am" is the philosophical answer to thta problem. It's the only certainty that can not be invalidated by untrustworthy perceptions.