Proof of Christianity

[Esquilax]

They've likely heard about color all their lives. Is that evidence of color? In your following example you seem to think so. Why do you say they're without evidence?

It's kind of a fine balance; there's a metric involved with apportioning belief to various things. Like, here:

Or more simply, just ask different passersby what object a color is and get the same response. That's all you're doing above, as the blind person must take the first sighted person's word regarding the colors of the boxes.

So, testimony from other people is sufficient to establish existence.

Not testimony alone, or at least, not for every claim. Claims vary in terms of believability, in accordance with what we know about the universe. I grant you, blindness and color is a more difficult example than most, but since sight can be demonstrated to a blind person fairly easily, the actual minutia of how that particular sense is perceived is fairly mundane. The claim of color doesn't really do anything to affect the life of the blind person you're proposing it to, nor does it really violate the laws of the physical universe, and so testimony might be enough to go on.

But at the same time, the reason I opted to go with the box test as opposed to just repeatable personal testimony was to remove as much subjectivity as I could; given enough time to familiarize themselves with the boxes by touch, any blind person could be shown that nothing differentiates the boxes aside from some additional perceptual thing they don't have, and the sighted person would be displaying knowledge that only the blind person should have, were they identical. It's a fairly objective test, and no, the blind person wouldn't be taking the sighted person's word for it regarding colors, because I propose using no references to color at all: just number the boxes. The sighted person will be able to identify what object is in what box by color, and relay that back using the numbers, or any other identifier one could imagine.

To the blind person, this guy has just walked into a room and correctly identified the contents of three identical boxes without opening them. The only way he could know that is if there was some difference between them that only sight could pick out.