Quote Originally Posted by hrst View Post
"Each layer in color film only makes one color and it is always fully saturated because there is no other choice. The density is the only variable I see."

That's true, but densities resulting in from a given scene is not only dependent on exposure. They are also dependent on spectral sensitivities of the sensitization dyes in film. AFAIK, this is the variable that controls saturation along with image-forming dye absorption spectra. But I would expect this is constant regardless of exposure. I might be wrong. But at least we can control this by selecting a different film. At least I would like to hear if there is more to this.
I agree that different films will have different color palettes. Ektar vs. Portra is a good example and that each film will have it's own unique response to any given input.

As I see it though, after choosing the film all we have control of are the densities involved.

My thought is simply that for any one given film there is only one color hue available on each layer and that when the three layers are "balanced and processed normally", the sum of the layers will always reach full design saturation.

I guess one way of saying this is that, even a perfect gray caught on color film isn't a monochrome or desaturated color, it's a fully saturated real world color created by a "balance" of density between all 3 layers.

We can manipulate contrast through composition, lighting, choosing the exposure relationships between our subjects and their settings, with polarizing filters....

We can manipulate the exposure relationships (balance) between the layers with colored filters to skew the densities one way or another to manipulate color balance. This is generally global though, with all the hues shifting say warmer or cooler, it may look better/provide better color contrast/be just what we want, but the saturation hasn't changed and our perfect gray subject from the scene is no longer gray.

Quote Originally Posted by hrst View Post
For example, it is known that when printing with sharp-cut RGB filters instead of CMY filtered white light source, saturation is increased because of less crosstalk between the color channels, and this is different from contrast. So, there are more variables in the play.
I agree that deviation from the normal processes and tools could easily change the palette a given film might produce.