01 Feb '10 19:30>1 edit
Originally posted by PalynkaMaybe, but less so in the daytime (pretty much everything is blue at night). In any case all that gentle ambient blue will help camoflauge blue food while the yellows and reds will stand out.
Wouldn't early humans see blue more often that reds and oranges because of the sky, the seas, rivers, etc? Fruits are rare (hence the advantage of perceiving red or orange as stand-out colours, or at least more than blue vs green).