When I was out riding like a zombie in the night, I spent a lot of time looking at racers' backs as we passed each other. And I thought to myself, "who the hell is that, and are they in my class?" All the solos had those rear yellow numbers, but everyone else had nothing.
So I would be stoked if more people got rear numbers with colors on them. It would be awesome if every class got a different color, but that would be like, 20 colors or something. Really useful for racers though! But, if that's too much hassle, you could start by giving the pair teams red numbers.
Basically what I'm trying to say is, when I riding into various trees at 11 am, it would have been nice to have a red number on my saddle so people knew why I couldn't ride a bike anymore
But also it would be cool to be able to know anyone's class -- or at least how many riders were on their team -- easily.