In October, 1951 - someone attending a taping of I Love Lucy brought along a color 16mm camera. (I guess studios were a lot more relaxed about such things back then).
The resulting footage, shot from the audience, is a fascinating artifact of what it must have been like to attend a TV taping back then. And today's video intersperses the 16mm footage with the actual broadcast episode. It's amazing.
For more details, the whole story is here.