How is Hue, Saturation and Brightness of colours explained via EM and QED? Light is a electromagnetic wave and its wavelengths determines the colour of the light, so that would be the Hue.

But what determines the Saturation. The less saturated a colour is the more greyish it becomes. How would you explain that with electromagniteics and with Quantum Electrodynamics?

And what determines the brightness of the colour? In QED I suppose it is the number of photons that's hitting your eyes? But how do you explain it with EM?
Also, some wet surfaces looks darker then when dry, how does that work. Why would less photons reach your eyes just because the surface is wet?

 A: You don't use EM or QED to explain most of this, because its more biology than anything.  Hue saturation and brightness describe perceptive color.  It's based on how the human mind perceives color.  Thus, the one bit of EM you need is this chart:

This is a chart of the sensitivity of the three color receptive pigments in the eye (plus the one used for low light vision).  When a wide spectrum of light hits your eye, each of the three color receptors responds to that light proportional to the integral of the number of photons of a given wavelength multiplied by this sensitivity curve at that wavelength.
After that step has occurred, the signal is now a data signal rather than a stream of photons, and our eyes process it as such.
Saturation - Saturation describes how much the signal appears to be a single wavelength.  If it is a single wavelength, then there will be a very particular set of RGB signals that can come out of it.  Our brain perceives this as saturation.  On the other hand, if the light does not have one wavelength that stands out above the rest, we will perceive it as desaturated.
Hue - If the color is saturated, then hue represents what wavelength the eye perceives as being the only wavelength.  This, of course, can be fooled by having 3 wavelengths carefully tuned to the colors our eyes are most sensitive to, which is how monitors work.
Brightness - The strength of the overall response. The more photons that hit the eye, the stronger the signal from the cones in our eyes, so the brighter we perceive it.

Also, some wet surfaces looks darker then when dry, how does that work.

This one actually is an EM effect.  Dry surfaces have a lot of rough edges which scatter light in all directions.  Wet surfaces have a smooth surface of water on them.  If you've ever been startled by the bright reflection of the sun off of a still pool of water, you have your answer.  Most of the energy that hits a wet surface reflects in one direction.  Thus, the object appears very bright in that one direction, and darker in all other directions.
