@downtide, to my inner eye, the vowels usually have warm colors (yellow, orange, red) and the consonants cool colors (blue, green, purple). But there are some chameleon letters that take color from their neighbors, and a very few are white, gray, black, brown, or colorless. Some single letters change color in different positions.
However, in spoken English, accents do tend to cast a tone over the words. A certain British accent, for example, gives sounds a yellow wash, and another tints everything slightly chartreuse. I hear some Southern American accents in bluish tones, and the speech of the Northeast has extra red in it.