Synesthesia is when two senses combine with each other and form relationships. For example, I have the most common kind: grapheme-color synesthesia. Mine looks like this. The only one that’s supposed to be black is “1”. Otherwise, the ones in black have no color associated with them.
I have a similar thing for checking spelling! Don’t write it in the air, but if I need to figure out the spelling of something, I just write it down and see if the colors are right. Works better in my native language than in English, especially because for some words the colors are “right” for American spelling, and for others it’s the British…