What are the colorants of the actual Bayer filter pattern used to filter the photons coming in to come up with the RGB filtered grayscale densities for each camera?
There is no such thing. It is important to understand, that
a. it is possible to create all or almost all visible colors with the mixing of at least three properly selected, fixed colors (primaries),
b. it is not sufficient to capture only such primary colors with the sensor; the sensor needs to capture *all* wavelengths. Thus the filters are not analogous to the phosphor or to the LED.
In fact, all three "colored" pixels capture the entire or almost the entire visible spectrum, but not all wavelengths equally. Any given wavelength can pass all three filters, but to different degrees in the three kind of filters.
As one would expect it, the red filter lets the light rays in the red range pass through to a higher degree, than other wavelengths (and even the different wavelengths in the red range result in different response). Therefor the three kind of pixels can be seen as the red, green and blue components of an RGB color and this way the original scenery can be reproduced quite well, but it does not come even close to the result of de-mosaicing and color transformation.
I attach two images, one converted by DPP with all neutral settings, the other is with the raw pixels interpreted directly as red, green respectively blue (white balanced on the same spot). Click on the thumbnails to see the larger image (a small crop of a 20D shot).
I added a third rendering: every pixel on the monitor shows only one color component, the one corresponding to the raw pixel's dominant color, the other two components are null. This is much sharper, but darker because of the lack of the two other color components. Furthermore, it is greenish, because half of the pixels are green.