Couple of options.
Run faster shutters that will just pick one. But some field of views can be problematic
Run a Day profile and a night profile and force day profile into color and night profile into B/W. Then either use the sunrise/sunset utility to adjust it based on location or set a schedule in the camera. The day/night profile management option works for some, but it can be hit or miss. When I tried that it, would end up picking a profile to run and then simply switch color or b/w but then with the wrong parameter settings.