I thought it said plenty. Admittedly I only read the first paragraph and went "oh, I get it". They're just things that are subjective, even if we nominally agree on an objective definition.

Like, we can all agree that a ketchup bottle is red, but what it really looks like to each of us might be totally different. My red might be your blue, but since your blue things are called red, and my red things are called red, we pretend it's just a single color, instead of a potentially infinite number of colors, a different one for each person.

Significantly, this hypothetical becomes real when we talk to, say, a colorblind friend. A ketchup bottle is still red, but it's definitely not the same red-- since it seems "closer" to colors that the non-colorblind would say.