I used to be a fan of the "Color of airplane" method, reasoning like others, that I couldn't see the tail number anyway. Until I realized, of course that something like 80%* of airplanes that would make this kind of call (i.e. flight school trainers) are white. And of course, much of the time you can't tell the color anyway.
While we can't read the tail numbers either, at least that lets you keep track of who's where. "Okay, Cessna 123 reported downwind a minute ago, so they're about to report base, Cessna 456 just called taking off..." etc. You can keep track that way.
* totally pulled out of my nether regions, of course