Synesthesia isn't just in your mind. The body reacts as if the colors were real.

A new study suggests that people with synesthesia have different pupil reactions depending on the colors they observed. . | ...
Psychology Today

Synesthesia, Semiotics, Semantics and How We Learn

Each person's perception is individually unique and subjective (Cytowic 2018.) Anesthesia is the phenomenon of no sensation. Synesthesia is the phenomenon of multiple sensations. Human senses include ...