I know someone who has synesthesia. They associate numbers and some letters with colors. I find it fascinating and tried to document it. Wonder if the associations will remain the same later in life for them.
1 dark
2 blue
3 red
4 green
5 blue
6 yellow
7 purple
8 brown orange
9 yellow
10 black
11 black
12 black & blue
35 red & blue
a = yellow
e = red
i = blue
o = 0
u ~= 0