How do you know if it is what it is

So for example, red is the colour red. But what if a person was born sees green instead of red, but since birth they were taught to call it red. How do we know if they see the right 'red' or the right colours?

Well, you really can't know. This is philosophy (a subsection called epistomology, or how we know what we know). It touches on science in the area of facts. What are they? Facts in science are those observations which can be repeated by other individuals who come up with the same observations. You know that someone else knows what red is when he describes the objects which he sees are red, and those which don't, and you determine that it matches your own observations. When this happens enough times, your induce that he and you are sharing something which exists for both of you, the observation of redness. If someone comes along and tells you something is red when you clearly see that it is not, or vice versa, then we conclude that his experience is not ours, and we may essay an explanation, such as color blindness, different sources of light, etc.

If they say RED, the actual color is RED but they see it as green.
If they say GREEN, the actual color is GREEN but they see it red.

http://www.toledo-bend.com/colorblind/Is…

this is an interesting short article that answers the question in better terms than I could, and with pictures.

The name of the color doesn't change its wavelength.

My 'crvena' and your 'red' are the same color.