Here's an excellent choice for color roundie demonstrations, 'A Star Is Born' from 1937:
https://www.youtube.com/watch?v=4h2s1elEYMQ
This copy was pulled directly from a Blu-Ray release done by Kino in 2012, and since the film is in the public domain, it ain't going anywhere any time soon. You can also get around copy right claims when posting demonstration videos to YouTube etc, by using something already in the public domain.
I have a DVD copy of this, and the picture quality on the DVD is terrible. While this still isn't perfect, it is much clearer, and perfectly watchable.