People are not born with the knowledge they are color blind. At some point early in their life they are given a test, like a red and/or green number against a gray backdrop. Most will see the number, some won't.
You are absolutely correct. I didn't know I was color-blind until my parents started getting negative reports about my behavior in school. My parents had switched me from public school to Catholic school that year, and the crayons used in class were big thick things with no labels on them. When I was in public school, I simply read the labels. I knew that sky was blue and grass was green, so I choose the right crayons. In Catholic school, with no labels on the crayons, I chose the ones that looked right to me. So my skies were purple and my grass was brown, and the teachers thought I was doing it on purpose to be disruptive.
And you are also correct about people 'telling you' about colors. I can't begin to count the number of times people have thought that if they just explained colors to me, I'd suddenly be able to see them. Trust me, it's like shouting at a person who doesn't speak English; your volume does not make them suddenly understand your words.
Getting back to the DAC, the fact is that some people can hear a difference and some cannot.
For the longest time, I thought all CD players sounded exactly the same. So I was pretty much of the opinion that it was all snake oil. Sorry, that's what I thought, based on my own ears.
However, I have since then heard some CD playback on modern day DVD players, once touted as good 'cheap' CDP, and they sounded much worse, even to my ears. So I get it. Different DACs sound different.
But for me, it takes a pretty large difference before I hear it. Quite a few of them still sound the same to me. Ooh, here's a Burr-Brown and here's a TI blah blah blah. Yeah, OK. If you say you can hear the difference, I believe you. But I can't. Just like being color-blind; it is what it is and I can't change that. Not even by 'careful listening' as some insist. I can't see colors I can't see by 'careful watching'. One either can or one cannot. My 2 cents.