Well, the thing about silent movies is that they usually didn't use the same title cards every time. To bring up Nosferatu again (just because that's the only silent movie I'm incredibly familiar with), there are several different DVD releases, and each one has a different set of title cards, so they're meant to be interchangable.

I guess basically what I'm saying here is, it's completely up to you. :P

If you want to make the cards the same colors as the scenes, then go for it, but just don't feel like it would be necessary. Personally, i thought those ones with the omnidirectional lighting looked great, especially the one in B&W, because with the light in the center it kind of looked like the light from a projector.