This one doesn't really have to do with writing, or anything, really. I just felt like talking about it. It's entirely possible that it won't be interesting to anyone but me.
You may or may not have heard of a condition known as synesthesia. Basically, it's when the wires are crossed with someone's senses. Some synesthetes can smell color, or see music, or taste sounds. I, meanwhile, have the more common and boring form known as color-grapheme synesthesia. To me, letters, numbers and words all have their own innate colors.
I'll start with letters. If you were wondering, K is orange. K is one of what I call the strong letters, that is, it has only one color normally associated with it. Other strong colors are A (red) and L (yellow). Letters like this very rarely change colors, even within the confines of words.
There are, however, second-tier letters that can have two or more colors associated with them. I'd say that most letters fall into this category. For example, there's R (red/brown) or S (green/yellow). These can change around depending on the word they're in, the letters that surround them, and even just what I'm feeling like that day.
The final type of letter is most rare. I can only really think of maybe four, E, F, T, and sometimes I. These are the chameleon letters. There isn't any particular color with which they're associated. They tend to take on the colors of the letters around them.
This brings me to words. Words for specific, concrete things will usually look like the things they are describing. For example, water is blue and watermelon is pink and green with little black pips. Other words normally take on the color of the first letter. Anarchy, for example, is red. If there are any particularly strong letters in the word, though, they will likely show up as whatever their color is. The word lesbian, for example, is mostly yellow, but there's a bright dot of blue right around where the B is.
Names are an interesting case. They tend to vary somewhat in color depending on who they're referring to. John in the context of John Green is very brown and green, whereas John my guitar teacher is brown, black and grey.
Finally, there are numbers. Each single-digit number, from 0 to 9, has its own color, although 2, 6 and 9 are all different shades of green. A double-digit number or higher will just have the two colors next to each other. 25 is a block of green and a block of red. 107 is yellow, a bit of white and some purple. I remember trying to count to one hundred once in kindergarten and getting distracted somewhere in the 60's by all the green going by.
Of course, the colors are all in my head. I'm still seeing the words I'm typing in black, even if I have a strong sense of yellowness every time I type the letter H. They don't really affect me all that much, although it's a little weird to write the letter A in a blue pen. They're just something I like to think about sometimes when I've got nothing better to do. Or, like now, when I have better things to do, but I'm trying to procrastinate. Better go do that work I'm putting off.