Can someone explain colorblindness?

Those dot charts where there's numbers or letters in different colors INSIDE the main circle is the basic test. If you're colorblind to blue, you can't see blue as a distinct color in the circle where it takes the same shading value with another color, for instance.

There's tests online, here's one link. https://www.eyeque.com/color-blind-test/

They can take a test designed to reveal colorblindness. Normally humans have trichromatic color vision, meaning we have photoreceptors in our eyes that can detect red, green and blue. Our eyes combine the different signals from these 3 types of receptors to allow us to see millions of colors. Color blind people and animals have fewer than 3 color receptors.

The photoreceptor cells have a pigment inside that is sensitive to one particular wavelength. It produces a strong signal if a photon with the same wavelength hits it, but it produces a much weaker signal when the wavelength of the photon is either longer or shorter. So, a red photon will produce a weak signal in the pigment that is tuned to green color and it will produce an even weaker signal when it hits the blue sensitive pigment. People who no receptors for infrared or ultraviolet light, so our eyes do not even see infrared or ultraviolet and mistake them as red or blue. Those wavelengths are no different when compared to darkness.

For example, most mammals can see blue and green color but not red. WHen they see red color, it looks green to them. So, to a dog, the red-yellow-green traffic lights will look green-green-green. The colorblind tests put red and green dots next to each other. To a colorblind person, they look like the same color. The red colored dots may be arranged in such a way that they show a letter of the alphabet or a number. However, a color blind person won't be able to see the letter or number if they cannot distinguish a red dot from a green dot.

It does depend on the type and degree but you can almost simulate it by turning the contrast down a lot on a TV. What you find is that colours all become washed out and so it gets hard to tell say, brown from orange green from blue etc. But a very pure red is still distinguishable from a very pure green and so on, thus a colorblind person can understand the meaning of certain colours to some degree, while others that are similar might be identifiable as a group but hard to separate individually.

What happens in colorblindness (I think) is that the frequency response of two different colour receptors in the eyes are too similar, which is effectively like turning down the contrast between just two of the primary TV colours.

A colorblind person can't (or has a hard time) telling the difference between red and green. Or between blue and yellow, there are various kinds of color blindness.

there are many kinds of colorblind some harder to detect than others .. one type is RED Green color blind ..

if they looked at a traffic light when it is RED it will look the same when it is GREEN I THINK it actully looks black but dont take my word for it . so that is the easiest type to detect ..