John Daltons original hypothesis for his deuteranopia was actually that the vitreous humor of his eye was discolored:

I was led to conjecture that one of the humours of my eye must be a transparent, but coloured, medium, so constituted as to absorb red and green rays principally... I suppose it must be the vitreous humor. An autopsy of his eye after his death in 1844 showed this to be definitively untrue, though other filters are possible. Actual physiological examples usually affect the blue-yellow opponent channel and are named Cyanopsia and Xanthopsia, and are most typically an effect of yellowing or removal of the lens. Tetrachromacy in carriers of CVD
Females that are heterozygous for anomalous trichromacy (i.e. carriers) may be tetrachromats. These females have two alleles for either the OPN1MW or OPN1LW gene, and therefore express both the normal and anomalous opsins. Because one X chromosome is inactivated at random in each photoreceptor cell during a females development, those normal and anomalous opsins will be segregated into their own cone cells, and because these cells have different spectral sensitivity, they can functionally operate as different opsins. This theoretical female would therefore have cones with peak sensitivities at 420nm (S cone), 530nm (M cone), 560nm (L cone) and the fourth (anomalous) cone between 530nm and 560nm (either M* or L* cone).If a female is heterozygous for both protanomaly and deuteranomaly, she could be pentachromatic.
Confusion colors for red-green color blindness include:

Cyan and Grey
Rose-Pink and Grey
Blue and Purple
Yellow and Neon Green
Red, Green, Orange, BrownConfusion colors for blue-yellow color blindness include:

Yellow and Grey
Blue and Green
Dark Blue/Violet and Black
Violet and Yellow-Green
Red and Rose-PinkThese colors of confusion are defined quantitatively by straight confusion lines plotted in CIEXYZ, usually plotted on the corresponding chromaticity diagram. The lines all intersect at a copunctal point, which varies with the type of color blindness. Chromaticities along a confusion line will appear metameric to dichromats of that type. Anomalous trichromats of that type will see the Chromaticities as metameric if they are close enough, depending on the strength of their CVD. For two colors on a confusion line to be metameric, the Chromaticities first have to be made isoluminant, i.e. to have the same Lightness. Note also that colors that may be isoluminant to the standard observer (typical trichromat) may not be isoluminant to a dichromat. Color tasks
Cole describes four color tasks, all of which are impeded to some degree by color blindness:

Comparative – When multiple colors must be compared, such as with mixing paint
Connotative – When colors are given an implicit meaning, such as red = stop
Denotative – When identifying colors, for example by name, such as “where is the yellow ball?”
Aesthetic – When colors look nice – or convey an emotional response – but don’t carry explicit meaningColor blindness causes difficulty in all four kinds of color tasks. The following sections will describe specific color tasks that the colorblind typically have difficulty with.