This kind of question is a lot more interesting to sighted people than blind people. There are two scenarios:

1. The blind person has experience with sight, either, as in the case with most blind people, that they still have some vision, or that they formerly had vision. So saying "hey, blind person, let us tell you about colors" is assuming a lot, chances are you're talking to a blind person who already knows the domain just like a sighted person does.
2. The case where you're talking about a person who was totally blind from birth, or totally blind so early they don't have memories of sight. Can't speak for all these people, some genuinely are interested in learning about colors in the gee-whiz sort of way that I think sighted people want blind people to be into it. "If I could also see that beautiful BLUE that you guys see." Really, though, I think this largely falls into a realm of, "who cares?"

Imagine if there were a group of people who could taste music. (Actually synesthesia is a thing, so these people probably exist in numbers.) That sounds pretty awesome, I'd like to taste music. But on the other hand you're probably only going to be mildly curious in their descriptions of their cool extra sense. It only sort of relates to the world you live in. You'd kind of be like, good for you, person who can taste music! And maybe you'd tolerate a discussion or two about them savoring a symphony with their palette or whatever, but it's not exactly essential knowledge.

There are two levels, I think, on which explaining sight to a blind person is actually useful, though to be honest most interested blind people are already going to grok this stuff already living in a sighted world. Those are

1. The level of the scientific, understanding what sight really is. So, essentially, light comes in wavelengths and can be measured in nm. If nm goes below 380, sighted people also can't see the light. Same if it goes above 780. So human sight is the experience of light between 380 and 780 nm. This is complicated somewhat by the fact that humans have three types of cones in the retina that are each sensitive to a different segment of the spectrum. they're call S, M, and L. So one is for the shorter end of the visible spectrum, one for medium, and one for long. This is why we have trichromatic vision, essentially we see three colors and then places where those colors overlap. This isn't really rocket science, it's pretty analogous to heat perception or sound perception.

2. The subjective experience of sight. Sighted people are really into sight and think it's super cool, and love to talk about evertything in terms of sight. This also include talking about sight itself a lot. Blind people have heard all this ad nauseum so they know that, for example, green in many cultures means go, red is the color of passion, black is scary because sighted people are scared of the dark, etc. So a lecture on the subjective experience of sight is pretty pointless and frankly boring, since life itself and having to hang out with sighted people all the time is essentially an extended lecture on the subjective experience of sight.

Hope that clears some of this up. I think this would be an easier question to answer if sighted people weren't so enamoured of sight and how super cool and magical it is. Get over it, dues.

Honestly, this is a much better question for people who are color blind, not those of use who are just blind. Color blind people have different concepts of colors (depending on what they currently see). Those of us who are blind, as has been said, either have seen colors and you're just kinda rubbing salt in the wound, or have never seen colors and literally don't care and you're kind of being a pest by bringing it up.