My brother and I also associate letters, numbers, certain words MBTI type and the Enneagram, etc. with colors.
I can remember doing as earlier as at least age seven, but I know it's not quite synesthsia.
My ENFP brother is a the same way.
What makes you think it's 'not quite synesthesia'?
If you consistently associate the same colours with the same letters/numbers, for no learned reason that you're aware of, it's very likely associative synesthesia. It's not all that uncommon.
1 - White
2 - Yellow
3 - Mauve
4 - Indigo
5 - Steel grey
6 - Green
7 - Pink
8 - Burnt sienna
9 - Pale gold
Isn't life under the sun just a crazy, crazy, crazy dream? Isn't life just a mirage of the world before the world? Why am I here and not over there? When did time begin? Where does space end? Where do you and I begin?
Level 5 4w5. Screw instinctual subtypes. (Ranking: 4>9~5>6>1~2>3~7~8)
Melancholic~Supine>Sanguine>Phlegmatic>Choleric Signal Patterns