We can't see color when it's dark because the photosensitive cones in our retinas that let us see color only work at certain light levels. Rods, another kind of photosensitive cell, let us see in black and white, and they can operate in conditions with less light--thus, we only see in black and white when it's dark.
http://en.wikipedia.org/wiki/Cone_cell
http://en.wikipedia.org/wiki/Rod_cell
That's my pragmatic scientific answer to the first question. As to the second, that will take more musing and mental chewing.