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.
This is my experience, anyway. I can't discredit you're experiencing, though, Costrin.
BlackCat, you may be on to something with the right-brain relatedness. Have you ever read any thing related to cognitive function and brain lateralization?
In psychology class, we discussed synethesia. Apparently, it's somewhat related to creativity.
Also, I read a book by Lenore Thomson that says types Introverted Judgement functions and Extraverted Perception functions all occur in the right brain.
Thus you and I would automatically be right-brained. Not to say that you are wrong, but may I ask, what makes you conclude that you are left-brained?
Here's my list:
One - Heather gray
Two - Cardinal red
Three - Navy blue
Four - Burgundy
Five - Midnight blue
Six - Dartmouth Green
Seven - Orange fruit
Eight - Black
Nine - Periwinkle
On a similar note, do you all have archetypes of each point of the Enneagram. For example, when I think of a Three, I imagine a really toned cyclist wearing sunglasses and a blue outfit. Another image is businessman in a sleek navy blue suite with his hair slicked back. The cyclist always has his mouth open with a look of deep thought on his face, while the businessman has a smile that makes him look almost untrustworthy.