You can assign a folder full of images to the background of Terminal.app, and it will choose background images at random, so a folder full of dark solid colors gives you random dark backgrounds, enabling you to tell your terminal windows apart easily.
In fairness, it's barely supported in Terminal.app --- in that I had to make a bunch of solid-colored images to make it work! It should be a first-class feature of all terminal applications. I had no idea how much I want this feature day-to-day until I got fed up with a 27" monitor display crammed with overlapping identical-looking tcpdump windows a few weeks ago.