that’s really neat!! i don’t know much about synesthesia, but it sounds like something that could really enrich your experience of the world.
i think i’ve been saying this a lot, but you could be a communications officer or maybe an officer in the command division who regularly goes on diplomatic missions. i don’t know if having synesthesia would make it easier or harder to learn languages, but the reason i think you might be suited for diplomacy is that your perspective as a synesthete could make you better than the average officer at understanding alien cultures that have crossed or unique senses