Probably need another post but...
Here’s my copy and paste with respect to cameras based on a number of conversations with Eric Walowit and Jack Holms, both on the ICC digital photo group.
Digital cameras don't have a gamut, but rather a color mixing function. Basically, a color mixing function is a mathematical representation of a measured color as a function of the three standard monochromatic RGB primaries needed to duplicate a monochromatic observed color at its measured wavelength. Cameras don’t have primaries, they have spectral sensitivities, and the difference is important because a camera can capture all sorts of different primaries. Two different primaries may be captured as the same values by a camera, and the same primary may be captured as two different values by a camera (if the spectral power distributions of the primaries are different). A camera has colors it can capture and encode as unique values compared to others, that are imaginary (not visible) to us. They don't exist and therefor are not colors. There are colors we can see, but the camera can't capture that are imaginary to it. Most of the colors the camera can see we can see as well. Yet some cameras can “see colors“ outside the spectral locus but usually every attempt is made to filter those out. More important is the fact that cameras “see colors“ inside the spectral locus differently than humans.
The point is that if you think of camera primaries you can come to many incorrect conclusions because cameras capture spectrally. On the other had, displays create colors using primaries. Primaries are defined colorimetrically so any color space defined using primaries is colorimetric. Native (raw) camera color spaces are almost never colorimetric, and therefore cannot be defined using primaries. Therefore, the measured pixel values don't even produce a gamut until they're mapped into a particular RGB space. Before then, *all* colors are (by definition) possible.
Raw image data is in some native camera color space, but it is not a colorimetric color space, and has no single “correct” relationship to colorimetry. The same thing could be said about a color film negative.
Someone has to make a choice of how to convert values in non-colorimetric color spaces to colorimetric ones. There are better and worse choices, but no single correct conversion (unless the “scene” you are photographing has only three independent colorants, like with film scanning).
Do raw files have a color space? Fundamentally, they do, but we may not know what that color space is. The image was recorded through a set of camera spectral sensitivities which defines the intrinsic colorimetric characteristics of the image. An simplistic way to think of this is that the image was recorded through a set of "primaries" and these primaries define the color space of the image.
If we had spectral sensitivities for the camera, that would make the job of mapping to XYZ better and easier, but we'd still have decisions on what to do with the colors the camera encodes, that are imaginary to us.
