I recently watched the video This Is Not Yellow explaining how red, green, and blue pixels can be used to create images of all other colors. Since yellow is created with red and green pixels, how is a person with red-green colorblindness (me, for instance) able to perceive yellow on a monitor?
Normal people see color due to the bellow mentioned combination of red, green and blue:
But due to genetic factors, The graph Distorts:
Now,If consider the normal Color code for yellow:
Yellow = R(255) + G(255) + B(0)
Or in other words
Max. Red + Max. Green + no Blue = Yellow
That means even if you can see a little of Red and Green, you can still a little deeper or lighter shade of yellow.
So Summing it up in the images:
Human color vision works because there are three different color-sensitive receptors called cones that detect short-wavelength light (bluish), medium-wavelength light (greenish), and long-wavelength light (reddish). The charts below show the sensitivity of these receptors in people with different genetics.
Chart taken from Color Art and Science, edited by Trevor Lamb and Janine Bourriau
The bottom chart, marked (c), shows the sensitivities of eyes of people with normal color vision. Short-wavelength (blueish) cones detect a distinct patch of light while the medium- (greenish) and long- (reddish) wavelength cones overlap, but are still separated enough to reliably distinguish between the two color ranges.
The middle chart, marked (b), shows mild protananomaly or deutananomaly color blindness in which the color regions that medium (greenish) and long (reddish) cones react to are more overlapped than in people with normal vision. This can lead to trouble distinguishing these colors since the overlap causes both receptors to light up for more colors.
The top chart, marked (a), shows complete protanopia or deutanopia, where the long (reddish) and medium (greenish) receptors completely overlap in their sensitivity ranges. This can also happen if one receptor is entirely missing from the retina.
I was under the impression that all red-green color blindness was of the protanopia/deutanopia type, meaning that the yellow generated on a computer screen should look red because the green light wouldn't be activating any of the non-functional medium (greenish) cones. In actuality, I only have a mild protananomaly/deutananomaly, so my eyes are still sensitive to the differences between red and green light, just less so than normal people. The yellow I see may be subtly different than other people, but I can still differentiate.
Enchroma glasses work for mild colorblindness by filtering out light in the overlap region of medium (greenish) and long (reddish) cones. This creates more separation in the detection region of those cones, thus making some colors more distinct at the cost of blocking some light.