I don’t know what you mean by “unidirectional relation”. I get that you gave an explanation after the colon, but I still don’t quite get what you mean. Do you just mean that what words I use doesn’t pick out a unique possible experience? That’s true of course, but I don’t know why you call that “unidirectional”

I don’t think describing colors to a blind person is nonsense. One can speak of how the different colors relate to one-another. A blind person can understand that a stop sign is typically “red”, and that something can be “borderline between red and orange”, but that things will not be “borderline between green and purple”. A person who has never had any color perception won’t know the experience of seeing something red or blue, but they can still have a mental model of the world that includes facts about the colors of things, and what effects these are likely to have, even though they themselves cannot imagine what it is like to see the colors.