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Very inaccurate summary, since I skimmed: Up to 12% of women have an X chromosome mutation that creates a fourth cone. This cone generally overlaps the spectral

Very inaccurate summary, since I skimmed: Up to 12% of women have an X chromosome mutation that creates a fourth cone. This cone generally overlaps the spectral region covered by the cones sensitive to red and green. The exact area of overlap determines whether or not each woman sees "more": If the fourth cone completely overlaps the region covered by an existing cone, no new information is presented to the visual system and the input is effectively discarded (she sees "just as much" red or green, not more, not less). If, however, the fourth cone has peak sensitivity in the gap between the cones covering red and green, she will she up to 100% more colour than women with normal vision.

Someone 11y ago
That's not quite correct. Where one cone type has a peak response, another may respond with a signal that is only one percent or less of its peak response, but the frequency regions in which hey have _any_ response basically overlap. Given the sensitivity curves, that difference is academic for blue versus red and green sensitive cones, but not quite for red versus green sensitive cones. What differs is the amount in which having a fourth type of come allows one to get rid of metameries (https://en.m.wikipedia.org/wiki/Metamerism_(color) https://en.m.wikipedia.org/wiki/Metamerism_(color), a term that the article surprisingly doesn't mention) If your fourth come type has a response curve that is very similar to one of te 'normal' three, there should still be _some_ effect, but it will be hard to devise an experiment that shows the ability to discriminate additional colors. But given the impact that not having red or green cones with their fairly similar sensitivity curves has, I suspect having a fourth curve, even if it falls between the two, will have a measurable (in the lab) effect on one's ability to discriminate colors.

Someone 11y ago

That's not quite correct. Where one cone type has a peak response, another may respond with a signal that is only one percent or less of its peak response, but the frequency regions in which hey have _any_ response basically overlap. Given the sensitivity curves, that difference is academic for blue versus red and green sensitive cones, but not quite for red versus green sensitive cones. What differs is the amount in which having a fourth type of come allows one to get rid of metameries (https://en.m.wikipedia.org/wiki/Metamerism_(color) https://en.m.wikipedia.org/wiki/Metamerism_(color), a term that the article surprisingly doesn't mention) If your fourth come type has a response curve that is very similar to one of te 'normal' three, there should still be _some_ effect, but it will be hard to devise an experiment that shows the ability to discriminate additional colors. But given the impact that not having red or green cones with their fairly similar sensitivity curves has, I suspect having a fourth curve, even if it falls between the two, will have a measurable (in the lab) effect on one's ability to discriminate colors.