[TheBigSalad]

Exactly, or maybe she simply saw a red apple in her dream. You can think if people as robots and the eyes are sensors that tickle the brain with the red signal. It can happen without actually seeing red. We know this because we have dreams and they are all sorts of sensory experiences that are completely made up by our computer brains.

[lolc]

I don't think people who have never seen red can dream of red. Color vision is acquired as far as I know. Newborns don't have it in the sense that they have to train to distinguish colors.

As such, I find it entirely plausible that Mary would be too old to learn color vision. Much like people born blind cannot acquire full vision later. She might just be unable to experience red. That would include her dreams.

Yes stimulatimg her optical nerves could prepare her to see red. Meaning she'd jave the brain hooked up the right way to see it.