I have extensive experience writing macros in Word's VBA language, and I'm convinced that you could write something which matched parenthesis sets and then color coded them, based on some behavioral parameters you'd have to code in there. (Such as: are indentations/spacing important or ignored? Do you want it to be just parens, or all types of brace-like characters? Do you want it to ignore comments? If so, what computer language is it, so that you can also put in comment ignoring and comment color-coding. Do you want it to ignore braces found inside string literals? If so, what are your string literal delimiters in your language, and if you're doing that well then you might as well color-code your string literals... it goes on and on.).

As you can see, though I know it's do-able, it would be a complex task as you'd essentially be writing a code language parser, and as such it would need to be language-specific. Word's VBA macro language would be up to the task I think.

If, however, Google isn't finding anyone who's already done it, then you might be the first person to need to do it in Word. In that case, have fun, you're on your own, there's no WAY I'm tackling this one for you. :-)

Note: I'm pretty sure it's going to be much easier to do it as a macro that you run, as opposed to something that you do on-the-fly while typing. In other words, run a macro to color-code your entire document, rather than expect it to color-code it on the fly while you type. Though VBA could do it, I don't expect it could do it fast enough for it to be realtime.

Now you've got my curiosity piqued. I could imagine someone who wrote coding books would want something like this. A section of code, in a book, if it were correctly color-coded, would be so much easier to understand than just plan black text. I wonder if someone's written such a thing.