Thanks for the very interesting question!

First of all, I want to note that color only exists in the brain. Without the brain, there is just light of different wavelengths being reflected by different objects. Seeing color, then, is a result of the human eye and brain detecting and processing light of different wavelengths. The brain also makes all sorts of guesses about what is seeing that go beyond the light it receives. For example, if you take a white snowball into a dark room, you will still see it as white, even though the snowball is no longer reflecting white light. This effect, called color constancy, is the brain filling in the color it expects objects to be.

What this means for your question is that our perceptions do not match reality. Furthermore, if our perceptions do not match reality, then our perceptions may not match each other’s. It is possible people may not experience the same wavelength of light in the same way. An extreme case of this would be colorblindness, where oftentimes people cannot detect the difference between reds and greens because they are lacking a certain type of cone cell in their retina.

At the same time, however, most people all over the world agree upon the properties of particular wavelengths. This is likely because the light that enters our eyes and the cells in the eyes and brain are uniform across most people, and so it is likely that most people perceive colors in pretty much the same way. For instance, people across cultures agree what colors appear “cool” and what colors are “warm.” So there are likely striking similarities in how our brains see the world, but also quite likely individual differences.

Light is a type of electromagnetic wave and the region of electromagnetic waves we can see is the visible spectrum. Within the visible spectrum, color is determined by the frequency of lights: the higher the frequency, the redder the light; lower the frequency, bluer the light.

Whether we perceive the same frequency of light as the same color is a matter of ongoing debate in the field of cognitive science, linguistics, and philosophy. However, we can determine which frequency our eyes response to.

Opsin is a type of light sensitive protein. Three types of opsin in human eyes are responsible for color perception, the L-cone, the M-cone, and the S-cone opsins. The L-cone opsin is most sensitive for long frequency, which corresponding to yellow; the M-cone opsin is most sensitive for medium frequency, corresponding to green; the S-cone opsin is most sensitive for short frequency, corresponding to violet.

Since the peak sensitivity frequency of L-cone opsin and M-cone opsin are so close, human eyes are very sensitive to green light. To imitate this, the light sensor array on a digital camera has far more green sensors than red and blue sensors.

We don't know that. This is a long-standing topic in philosophy, along with whether or not the difference between your red and mine actually matters. Recent research (explanation too long for here, but a good summary is in this article ) may even imply that we don't see colors the same way. As described in answers to a similar question on ScienceLine, one could also consider differences due to physiological variation, such as that which causes color blindness, as well as differences in at least perception due to past experiences (though I think these are subtly different from the intent of the question).

We don't know if everyone sees colors the same way. While we do know that colorblind people do not see the same colors as non-colorblind people, we don't know if non-colorblind people all see the same red as red, the same yellow as yellow, and so on. Some people can actually see more shades and hues of colors than other people. We might be able to measure how each of us sees color by using some scans of our brains, but that may not work completely, either. We might never know how differently we see colors, so imagine how differently we might see everything else! However, this does not have to be a bad thing. We are all different but we can all talk to each other and understand each other, and isn't that great?

We don't know whether we all see colors the same.

Some people are color-blind, and they don't see colors the same. I searched google for 'color blind test' and got all these cool images that show dots in different patterns that you can see if you're not color-blind for the colors in the images.

see here.

My old eyes are slowly getting cataracts, so colors aren't as bright for me now. I don't know of any measure to compare the dimmer colors I see with the brighter colors my granddaughters see - or with the colors my adult children see. I only know when I looked through the kaleidoscopes I bought many years ago, the colors were dimmer than I remembered.