Colour vision is based on an opponent process [1]. There are three kinds of colour receptors called L, M and S (for Long, Medium and Short) and they are recepti

Colour vision is based on an opponent process [1]. There are three kinds of colour receptors called L, M and S (for Long, Medium and Short) and they are receptive to colours centred around the red, green, and blue parts of the visible light spectrum respectively. Here is a good graph showing how sensitive each receptor is to different wavelengths of light: http://en.wikipedia.org/wiki/File:Cone-fundamentals-with-srgb-spectrum.svg http://en.wikipedia.org/wiki/File:Cone-fundamentals-with-srg... But we don't perceive colour directly from these receptors. Instead, our visual systems combine the output of these receptors to form three channels: black vs. white (L+M+S), red vs. green (L-M) and blue vs. yellow (S-(M+L)). This is why there is no such colour as a reddish-green or a bluish-yellow; our visual systems are not able to perceive these (except under exceptional laboratory conditions). As you can see in the graph, the L, M and S receptors aren't just receptive to pure red, green and blue but to a range of wavelengths centred near these colours, and they all overlap to some degree. But the L (green) and M (red) receptors overlap quite a bit. In red-green colour blindness, either the L or M are shifted so they're even closer. This means that the red vs. green (L-M) channel is no longer able to distinguish between the two, so this channel is always close to zero and the person no longer sees either red or green just something muddy in between. Blue-yellow colour blindness is similar, but in this case it's the S channel that's shifted towards the L and M. In this case it overlaps with both and this means there's no longer any colours that activate the S without also activating L and M (and vice versa), making it impossible to distinguish blue from yellow. For more information: http://en.wikipedia.org/wiki/Opponent_process http://en.wikipedia.org/wiki/Opponent_process These glasses work by notching out the parts of the spectrum where the receptors overlap the most. Assuming this works as described, they claim that this increases the relative difference between their outputs, making it easier for colour blind folks to distinguish the colours.