[old_tv_nut]

I just fast forwarded through it to see the production techniques.

Things I noticed:

Use of blue screen:
1) In the opening, where you see a typical failure in the threshold setting, and one of the dancers is partially and intermitently transparent.
2) In the scene where Drosselmeyer produces the mice.
3) In the final scene where the princess and prince are in front of a background scene that gradually fades out to the blue screen itself.
RCA had fashioned a way to use the blue channel of the TK-41 camera as a keying signal. Unlike modern keying, where the key color (usually green) can be selected as a hue and saturation as well as brightness, this blue key was dependent on the blue channel amplitude only.

Wavy dream (or watery) effect: done by adding an audio sine wave into the camera horizontal sweep. This had been used previously in monochrome cameras. Probably not the first use in color, but possibly. You can see that it was installed on only one color camera here, as it abruptly disappears when cameras are switched.

One other thing still notable in 1958 was the use of fixed focal length lenses and dollying, rather than zoom lenses.