The argument is called “Mary’s Room”...I prefer the more plausible and philosophically equivalent variant discussed above, although it drifts away from the etymology of the argument’s name
To be precise, the argument itself is called the Knowledge Argument (KA); “Mary’s Room” is a name for the thought experiment Jackson used to present it.
Actually, it was one of two similar thought experiments in Jackson’s original paper: the other one concerned a character named Fred who could see more colors than normal humans.
To summarize the linked article: Most people have three distinct kinds of photoreceptors that react to different frequencies of light: one receptor that is most sensitive to red, one receptor that is most sensitive to green, and one that is most sensitive to blue. (You can tell what color something is by the differences in the strength of the responses of the three different photoreceptors.) Genes for the red and green receptors are present on the X chromosome, so men have only one copy. Colorblind men have an abnormal version of one of these genes, so instead of getting a gene for seeing red and a gene for seeing green, they end up with a gene for seeing red and a gene for seeing a slightly different shade of red (which is why they can’t tell the difference between red and green). On the other hand, if a woman has one copy of the “defective” gene and one copy of the “normal” gene, she could end up with four kinds of color receptors instead of the normal three: the one for red, the one for green, the one for blue, and the one for the slightly different red. This would let her see a difference between colors that look identical to people with normal color vision.
To be precise, the argument itself is called the Knowledge Argument (KA); “Mary’s Room” is a name for the thought experiment Jackson used to present it.
Actually, it was one of two similar thought experiments in Jackson’s original paper: the other one concerned a character named Fred who could see more colors than normal humans.
He really should have reversed the names. Colorblindness is more common in men than women, and it actually is possible for a few women to see an additional primary color.
To summarize the linked article: Most people have three distinct kinds of photoreceptors that react to different frequencies of light: one receptor that is most sensitive to red, one receptor that is most sensitive to green, and one that is most sensitive to blue. (You can tell what color something is by the differences in the strength of the responses of the three different photoreceptors.) Genes for the red and green receptors are present on the X chromosome, so men have only one copy. Colorblind men have an abnormal version of one of these genes, so instead of getting a gene for seeing red and a gene for seeing green, they end up with a gene for seeing red and a gene for seeing a slightly different shade of red (which is why they can’t tell the difference between red and green). On the other hand, if a woman has one copy of the “defective” gene and one copy of the “normal” gene, she could end up with four kinds of color receptors instead of the normal three: the one for red, the one for green, the one for blue, and the one for the slightly different red. This would let her see a difference between colors that look identical to people with normal color vision.