I've actually done that with text before - in particular, ensuring that links in a document had the same URL in their text content as in their href - by making

I've actually done that with text before - in particular, ensuring that links in a document had the same URL in their text content as in their href - by making one red and one green (and putting them in a monospace font for good measure), you can see straight away when they don't match. I went with red and green because I intended to try using 3d glasses, but as it turned out, 'vaguely pinkish' was enough to see a match without actually looking.