Ineffable Ontological Detanglement .: Introspective Assistance & Mental Analysis Manual
Seeing sound as colour, tasting words and letters or seeing them as colours, tasting numbers or mathematical concepts or seeing numbers or mathematical concepts as colours. It isn't a brain fucked up signals got crossed, everyone who has it can see that they're looking at something well beyond brain glitching. It comes with genius, when you have a genius in a certain area, your brain taps into mysterious awareness territories where your capabilities enter the unconscious ethereal blur.
It's objectively subjective, different people feel it differently however they're all looking at an angle, the particular way in which they approach their genius means they are observing a different area of the blur. It is based purely on your core, your natural personality expression. It has nothing to do with your experience, it has nothing to do with your education, it has nothing to do with your mental conditions or mental atmosphere.
No, it is not a hallucinatory experience, not sober anyway. Anybody who tells you it is a hallucinatory experience is either lying or has some other form of hallucinatory crazy.