When I found out about the concept of synesthesia—linking colors to letters, for example—I thought it sounded like the coolest thing in the world, almost like a superpower. I wanted to be able to see colors when I heard music. Unfortunately, it’s not something you can get just by willing it.

You can imagine my surprise when several later, my younger sister found out that we did have a form of synesthesia. Ever since we were little, both of us have thought of numbers and letters as being either male or female. To me it was just natural and I was rather surprised that everyone didn’t do that. I think of some of them as having colors too, although that is not as clear-cut.
Numbers
In my mind, the numbers 1, 3, 5, 8, 9, and 0 are male. 2, 4, 6, and 7 are female. The male numbers are mostly a blue or purple color , since I think of those as male colors, while the female numbers are all yellow or red.
It’s interesting when I think about numbers above single digits. 1 and 0 are male, but not strongly so, so 12, 14, 16, 17 are clearly female. However, something like 25 is not as clear in my mind. I would still say it’s male though, which seems to indicate that the gender is determined mostly by the last digit.
Letters
For letters of the alphabet, B, D, E, G, J, K, L, O, P, R, T, U, V, W, X, and Z are strongly male. A, C, M, N, S, Y are strongly female. The others, F, H, and I are a bit fuzzier in my mind; sometimes they seem male, other times they seem female. Are there such things as androgynous letters? Possibly.
The funny thing is, that my sister’s breakdown of the genders of the numbers and letters is totally different from mine. Actually, it’s almost exactly opposite. I’m not sure what that means, but I find it very interesting.

The ones without colors don’t have a particular color strongly attached to them.
Other types of categorization
Of course, there are many ways to visual or categorize the world. Some people think of different sounds as having colors. My anthropology professor in university grew up Africa where there is a rainy season and a dry season and so he naturally categorized all colors into “wet” and “dry” colors.
One strange thing I do is to categorize things by two micro machine trucks that I had when I was younger. One was blue and the other was yellow and red. My best friend used to play mostly with one and I would mostly play with the other one. I began to associate them with aspects of our individual personalities and then began to expand them to other things. It’s hard to pin down exactly what each represents, but in general, the blue one is more conservative and introverted and the red and yellow one represents more innovative, out-going things.

These are the closest I could find pictures of. The bottom ones looks spot-on.
Is there any distinct way that you perceive life? Have you had similar experiences to me? I’m curious.