« Description of colourblind conditions »

The known forms of colorblindness

Normal vision

Trichromasy
All three cones types are present and working normally

Mildly colour blind

Anomalous trichromasy
A mild colour deficiency or weakness affecting 6.3% of men and 0.37% of women. One or more of the three cones light sensitive pigments are not quite right, affecting the balance and brightness of colours:

Protanomaly
Mild trouble with red. Red, orange, yellow, yellow-green, and green are muted and look more like green. Other colours can be affected too due to filtering, thus violet appears blue.
This affects 1 in 100 men

Deuteranomaly
Mild trouble with green. Again, he (or far less likely she) is poor at discriminating small changes in red, orange, yellow and green, however, unlike the above example the various hues shift towards red. More importantly for the individuals, they do not suffer the loss of "brightness" problem.
This affects 1 in 20 men.

Tritanomaly
Mild trouble with blues. Persons affected by this condition have difficulty distinguishing between yellow and blue.
This is rare, affecting only 1 in 10,000

Seriously colour blind

Dichromacy
Complete loss of one cone type.
This is a severe colour deficiency affecting 2.4% of men and 0.03% of women:

Protanopia - long cones abscent. Unable to recieve red.
The brightness of red, orange, and yellow is much reduced compared to normal, with reds seeming black instead. Similarly they can't tell shades of blue.
This affects 1 in a 100 men

Deuteranopia - medium cones absent. Unable to recieve green.
Similar to above, but without the abnormal dimming. Red, orange, yellow, and green all look like the same colour.
This affects 1 in 100 men

Tritanopia - short cones absent. Unable to recieve blue.
...
This affects 1 in 1,000 men

Totally, truly colour blind

Rod Monochromacy
Truly colour blind They can only see in black and white.

Rod monochromats, or complete achromats, are truly "colour blind" since they cannot distinguish any hues (e.g., blue, green, yellow and red). They see only different degrees of lightness. For them, the world appears to be shades of gray, black and white. They also have poor visual acuity, aversion to bright light and nystagmus (an involuntary, rapid movement of the eyes).

Blue cone monochromacy is a condition in which the long and medium cones are missing, leaving just the short cones and the rods. Because these short cones do not contribute to our perception of brightness, blue cone monochromats have the same problems with bright lights as do achromatopes, although they are able to distinguish a small range of colors.
Fortunately monochromacy is extremely rare, affecting about 1 in 30,000 to 1 in 100,000

Others of interest: Tetrachromats

Tetrachromats
People who have four color pigments instead of the usual three!

Scientists are supposedly searching for such a woman (Genetics rules men out of the theory).
I've included this for interest though there's precious little on the topic. Such a person, it is believed, would have virtually perfect vision. I assume the extra cones would be yellow, though in nature these can be violet and ultra violet, perhaps other colours.
This affects ? Unproven so far. Bees are supposed to see tetrachromatically though and can see into the ultraviolet range.

Others of interest: Pentachromats

Pentachromats
Insects (and birds) that have five colour pigments.

This is in the realms of sci-fi and future gene manipulation. Far as I can tell such a person would see from far ultraviolet to infrared. Only stage after this is Superman with his x-ray vision and laser eyes!
This affects ? This isn't natural in humans. Some insects and birds to see Pentachromatically though.

Note, the figures are a rough guide. For instance once expert resource said "between 1 in 15,000 and 1 in 50,000" for tritanopia. Everyone seems to agree on the overall 1 in 12 figure though. I imagine the rarer conditions vary wildly from country to country.