Because of the tail of an absorption at around 750 nm absorbs the red. The absorption is an overtone of the O-H stretching vibration.
Interestingly, heavy water (D2O) is colourless, because the absorption band is at a longer wavelength (~950 nm). -- DrBob
Is it possible that this is connected to the origin of the term "blue laws"? I read something on encyclopedia.com about "blue paper they were written on," but that assertion seems asinine at best. A linguistic connection to German immegrants just feels more probable.--BlackGriffen
What are "blue laws"? Maybe they should be mentioned on the main article as well. --AxelBoldt
http://www.snopes.com/language/colors/bluelaws.htm
Food for thought, --Alan D
Another example of that would be blue blood. I have to wonder about the etymology of the phrases, though.--BlackGriffen
There are only "blaue Briefe" (blue letters) in German. Those are unpleasant letters parents get from school. --Vulture
In German, "blue" means "drunk".
"blau" is drunk, not "blue"