This is more of a curiosity, but I have often wondered if there are any common patterns to synthestesia, and now there is some research on it.
As a kid, I was curious why I never heard anybody talk about the color of words and sounds. Seemed much easier to remember things that way, such as words in a foreign language. And when I at one point mentioned that Mondays are blue and Tuesdays are yellow-orange to a friend, and he didn’t understand what I was talking about, I realized that not everybody associate color and texture with words, sounds and smells.
For me, Mondays are dark blue with a more gritty texture and areas of a translucent glowing green. Tuesday is yellow and orange. Wednesday a medium dark blue. Thursday red with some orange and yellow. Friday green with some yellow. Saturday dark blue and black, with some translucent overlays of color. Sundays yellow.
The letter A is red with some orange and yellow. B is blue-green. C is lemony yellow. D is yellow towards orange. E is medium blue. F is mossy green. G is metallic blue. H is green. I is light yellow. And so on. Most vowels are yellow, red or orange, and most consonants blue, green, or other darker colder colors.
From the Science Daily article on commonalities in synesthesia:
Interestingly, they found that the particular pairings are determined by how frequently graphemes and the colour terms are used is used in language: common letters (e.g., “a”) pair with common colour terms (e.g., ‘red’) and uncommon letters (e.g., ‘v’) pair with uncommon colour terms (e.g., ‘purple’). This shows that perceptual synaesthetic experiences are influenced by environmental learning.
A is red for me too. V for me is a faded grey, maybe because it is less used in my native language.