The canonical example of this kind of problem is the shape of a strawberry bush. It is easy to learn to recognize what a strawberry bush looks like, nearly impossible to describe in words. It simply is not true that explicitly held concepts are necessary to perceive and judge similarities and differences at the perceptual level. You do not need to have a concept of color to see color, or a concept of length for length, or every human and every animal would be blind.
Colors, lengths and shapes are epistemological givens provided to us by the automatic operation of the senses, and in the