toning for the illusion of extended dynamic range, etc.

Is anyone out there really up on their color theory?

We all know that various toners have measurable effects on the density of the target print--some reduce density like sepia, others build density like selenium. This has measurable effects on the dynamic range and often these effects play out in feelings of "richer shadows", etc. For posterity, we should throw in that different toners affect the shape of the highlight/midtone/shadow curve and thus local contrast in the print (proportional/superproportional/subproportional intensification/reduction).

Playing with duotone in photoshop got me thinking about the effects of different colors on the _perceived_ dynamic range aside from true changes in density. For instance, a blue tone versus a yellow tone under controlled conditions might have the same grayscale density, but the yellow is percieved to be brighter. This is in part because our eyes are far more sensitive to colors in the yellow and green wavelengths than to larger or shorter wavelengths (reds out to IR and blues out to UV). There is a bell curve of color sensitivity for the human eye.

So I'm asking, what can we do with toning to leverage the differing sensitivity of the human eye? Can we trick the eye into believing there is a larger dynamic range on paper than is truly represented, perhaps by using toners that tend toward yellow? Would a color for which we have a high sensitivity (yellows/greens) appear to spread color values better across equivalent density values than say "dark" colors like red and blue/purple? Would using a "dark" color trick our eyes into thinking that a high portion of the values are bunched up in the shadows, perhaps leading to a feeling of rich shadows or well differentiated highlights (I'm not sure which would be the case)?

What are the effects of color, outside of a change in density, regarding toning? What can we do with this? What do people do with this already? I'm particularly interested in how people leverage human color perception to create effects which could not be duplicated, or would be less effective, with a pure neutral grey scale. I'm trying to get a grasp on this simply as part of learning to visualize and create a better print.

In researching this on the web I found a 1940 letter from Ansel Adams that touches on this. (Photo Notes, 1940, http://newdeal.feri.org/pn/pn6740a.htm) Basically he says a little bit of toning makes perceptual changes that a densitometer doesn't fully capture.

---
"I believe that a moment's thought will convince one that the particular blue-green-black of the usual photographic print is a color that is definitely "negative" in itself. It is peculiarly "dead" and the average print suffers through this inevitable "negative" black. For reproduction purposes, there is very little value in tone control, as the ultimate visual effect is what counts, and most printing processes are not so hot. But considering the actual print--the print as a thing in itself--I believe you would be astonished if you could see the difference between an ordinary print and a slightly toned print. The actual tonal relationships are imperceptibly changed--but the color of the print; the visual impact of the values; is vastly improved. The illusion is that the scale of the print is augmented. This augmentation I do not believe the sensitrometric devices would respond to, as, weight for weight, the tones remain about the same. But the peculiar purple-brown tone--very slight--that is obtained by only a few minutes treatment in the toning bath, does wonderful things from an emotional point of view. Try it sometime! But never carry it so far that the toning is obvious."
---

Thanks in advance for your thoughts and experiences.