Chox, the planes in the film are a mixture of specially built replicas, and more "modern" types that were dressed up for their parts in the movie.
The Pfalz, Fokker D7's and Triplanes were full scale replicas built for the movie. They only built a few, so French SV4 biplanes were painted in Flying Circus colors to fill up the sky behind them. I think it was all really well done, and even knowing all of that, anytime I see this picture, it still doesn't bother me.
The SE-5's are interesting, in that they are not full scale planes. They were 85 percent scale, but no matter how many time I've seen this movie (and I've seen it plenty! I used to own a VHS copy, and lost it) I still can't tell. They stuck Lewis guns on the upper wings of some of the SV-4's and painted them brown, to fill up the British air scenes, too.
An old French trainer called a Caudren(did I spell that right?) 277 served as both an RFC two-seater, and a German two-seater.
Great movie, isn't it? I NEVER get tired of watching it.