Very interesting discussion! Last semester, I took a course called "Color Theory" and here's the best way I can explain it:
Color and photography share similar principals in that they are both based on interpretations of light. Colors come from the spectrum of light, with each color producing its own unique wavelength signature. Receptors in the human eye are not capable of processing all of these wavelengths, and as such, cannot see all colors visibly (ultraviolet and infrared for example). Because the human eye is not standard (meaning everyone has a different set of eyes) not everyone will "see" the same colors.
The wavelength (color) that is produced is the result of a few different factors, including a subject's absorption
and reflection properties. This means that a similar color will appear differently on different objects. The exact same wavelength frequency that produces red will look very different on a wooden barn versus an automobile for example.
Color theory works with HSL: Hue/Saturation/Lightness (RGB sliders in Photoshop can be changed over to HSL).
- Hue: a color's direction on the color wheel from white. Hues are the color's name, such as green, red, yellow, etc.
- Saturation: a color's intensity. Bright red is considered more saturated.
- Lightness: refers to the amount of black or white in a color. Maroon adds black to the red hue, while pink adds white.
Now....all the technical stuff aside and how this affects f/stops....I'm sure you can all figure this out. By changing f/stops you are allowing more or less light to enter the camera, which can change color values significantly. This would generally apply to manual mode, because the shutter compensates in AP mode and you wouldn't notice much difference.
Here is an interesting color experiment from this class:
One color as two:
Notice how the red color "A" appears to be different when placed against these backgrounds? The same with color "B". This experiments shows that our eyes make a color's overall distinction in comparison to its surroundings.
Two colors as one:
The opposite is also true. Colors "C" and "D" are different, but appear to be the same here. So do "E" and "F".