The point is that even the claim about the connection between the crystalline structure that exists in reality itself and produces the color, and the color itself, is also built on the concept of crystallinity and the concept of connection.
All these things as well have no basis in the reality around us. So the connection between our understanding and the reality around us is not clear.
(The example I gave of a person with good character traits referred to point B.)

There is a misunderstanding here of what I explained.
The concept of crystallinity also exists in the world in some form, and its image in us is described in our terminology. And again, it makes no sense to ask whether there is a connection between the two, because of course there is a connection: what is called crystallinity in the world produces in us an image that we call crystallinity. Think of a creature that is built differently, and from its perspective there are no visual images at all, only other senses. For it, the world would not be represented visually but in some other way, for example acoustically. Would there be no correspondence for it between reality itself and what is in its consciousness? Of course there would be correspondence. It would be just as right as we are. Both it and we describe the same picture in two different languages, like Hebrew and English. In both its case and ours there is correspondence between the world and the picture (audio or video) in consciousness.

Rabbi Michi, what do you mean by "the traits are inside the person, inwardly, and it is hard for us to know anything about them directly"? I think good character traits are simply behavior that arouses in us the feeling, "this is good" or "this is bad." What is there to understand about them?

Not at all. Traits are qualities and character within the soul itself. Behavior is at most an expression of the traits, and even that not always (since traits do not dictate behavior. We also have choice, and character does not determine behavior fully).
I have written about this here more than once, in resolving the difficulty raised by Rabbi Chaim Vital and Rabbi Abraham Isaac Kook, who asked why the Torah does not command the refinement of character traits and went on at length in their own way to resolve the matter. And in my humble opinion I did not understand it, because the Torah does command it: to cleave to the traits of the Holy One, blessed be He, and this is a counted commandment according to all the major enumerators of the commandments.
In explaining the matter, I wrote that what we are commanded is to cleave to His modes of conduct in practice (attributes of action), because only that is revealed to us. But refining one's character traits does not refer to behavior, but to our inner character and inclinations. About that there באמת is no commandment. And this is not the place to elaborate.

Okay, I see that the way I phrased my words was not good.
What I mean to ask is: what is there to "understand" about traits in themselves? What is unclear about them? Isn't the criterion for whether a trait is good or bad that same inner feeling ("intuition") that trait A is bad and trait B is good?

You asked about what I said. I was talking about the ability to know someone's traits (diagnosis), not about understanding the meaning of the trait itself.

Ah, sorry. Then I didn't understand what you meant.