Glasses That Hack Around Colorblindness

There are two different types of red-green color blidness, basically resulting from the lack of functional red or green cones. Both red and green cones are sensitive to red and green, but in different amounts. Missing one type (or having a very low count of active cones of one type) won't make you blind to that color (i.e., objects painted with that color won't appear as black), it will just make you unable to distinguish reliably between the two hues.

That's why color-blind "simulations" typically show yellow (because it's what you get by mixing red and green). In reality, most color blind people see in red-blue or green-blue (in terms of signal) - though both red and green overlap onto yellow and even onto each other at cone level. What those people call it internally (red, orange, yellow, green) is up to them; mostly they'll try to figure out (from experience) what a trichromat would see, and they'll call it that.

If you look at a cone spectral sensitivity curve, it should be pretty obvious. The brain only gets three signals, but each signal is actually reporting a wide range of frequencies, and they all overlap to some extent.

The OP is wrong, BTW. Color blindness is due to defects in the eye, causing one or more foveal cone types to be missing or inactive.

The after image effect he mentions is from a study that showed that partially color-blind people (generally termed "color weak") can sometimes distinguish the hue of after-images better than they distinguish the hue of the original image. In some cases, this means people who are just (very) color-weak can be classified as color-blind by basic Ishihara tests. That's where the visual cortex plays a role (by making some hues more "relevant" than others). It doesn't change anything about the actual eye defects.

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/JAd5kWwlb3Y/story01.htm

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