As you can see in RAW data histograms, Green and Red are balanced perfectly (without any filters) in incadescent bulb light. You don't want to use any filters in this low-light condition, anyway.

Also, I don't think that 'gamut' is a good word in describing digital camera. Camera is sensitive to any visible light (to infrared - too), so camera gamut is equal (or broader) to human gamut.
We should describe camera behavior in terms of metamerism: some colors cannot be separated (i.e. same RGB(G) response for different colors)