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
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