From the histring README:

This program simply highlights strings using ANSI terminal escape codes. It
started out as sample code for using regular expressions but it turned out that
I used it so much that I thought it warrented a release.

One of the most common things I use the program for is helping me parse the
output of grep and diff. I think that this programs functionality should be
folded in to those programs but until then histring does the job nicely.

WWW: http://ess4.engr.uvic.ca/proj/histring/