Why do things look darker when wet?

[Alex Franke]

...except paint, I guess, which gets darker as it dries, it seems like most things appear a little darker when they're wet -- like hair, wood, counter tops, etc.

My little boy asked this questions, and I couldn't come up with a good answer... Any ideas?

[Uncle Cracker]

Most materials absorb more light when wet, thus the darker appearance. Light colors are much a result of reflection in the visible spectrum.

[smorris]

Some of the light that hits the water will pass through. When it does, it will be refracted (bent), so that its path changes. When light from the object is emitted, some of it will again be refracted as it passes through the water again.
Not all of the light that is emitted that would have reached our eye now does so, because some of it has changed direction.
In other words, because there is less light coming from the wet area (some was refracted in a different direction), that area will look darker than the material around it.