We do have four sectors, 3 color perception and then the brightness perception that is used in the dark. In mid darkness you get a mix of all of those, although the fourth is not really perceived as a color so it can be a bit hard to use.
Brightness is another dimension, not a "sector" (as I dubbed it) on the color spectrum. But it would be equal for all subjects in a test, so it can't add information.
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We do have four sectors, 3 color perception and then the brightness perception that is used in the dark. In mid darkness you get a mix of all of those, although the fourth is not really perceived as a color so it can be a bit hard to use.
Brightness is another dimension, not a "sector" (as I dubbed it) on the color spectrum. But it would be equal for all subjects in a test, so it can't add information.