Color Blindness Simulator

[korn1]

Pretty cool

[reedOsama]

Protanopia with traffic lights... Red light means caution

[Lycanthrope]

This brings another question in mind that we can't really answer. How do we know that the colour green I see is the same colour green you see, or any other colour for a matter of fact?

The retina contains two major types of light-sensitive photoreceptor cells used for vision: the rods and the cones.
Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision; they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are none at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina.
Cones are responsible for colour vision. They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are mostly concentrated in and near the fovea. Only a few are present at the sides of the retina. Objects are seen most sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are stimulated by light, they connect through adjoining cells within the retina to send an electrical signal to the optic nerve fibres. With the result that the optic nerves send off impulses through these fibres to the brain.[43]

http://en.wikipedia.org/wiki/Eye#Rods_and_cones

Essentially, colour-blindness occurs when either the photo-receptors are faulty (usually congenitally) or the eye, nerve or parts of the brain becomes damaged.

You know that you see the same colour I do based on the fact that our eyes perceive colour using the same physiological mechanism. If there is something wrong with that mechanism, you experience colour-blindness.

[asidsoul]

Little off topic, but i had a friend that was a manger at a restaurant, and one day 2 couples came in, and immediately he could see something was different about them, because the were signing like crazy to express themselves. Them he had an idea, and brought them braille menus... to which they just stared at him...