Production Switchers

How do I program a key to take a camera feed from color to black-and-white and transition back to color

You need to do a split key. Put the BG source in your key, make it white (or yellow for sepia), then hold down the Auto Select or Self key buttons (one or the other, doesn't matter) and select the camera you want to use from the source selection row. Then you can switch that key in any way you want, but make sure you have black on program behind it.