Take the tour ×  A recent XKCD comic implies that the sky is
blue as opposed to violet due to human physiology, and that
animals more sensitive to shorter wavelengths will perceive the
Earth's sky as the shortest wavelength that they can comfortably
see.  Is this phenomenon also responsible for relativistic blue-
shifting, as opposed to relativistic violet-shifting? In other
words, might different creatures perceive bodies approaching
them as violet or even shorter-wavelength colors that humans
cannot see?  share|improve this question Blue shifting is just a
term which implies that the apparent wavelength of light that we
receive is becoming shorter with time, or moving toward the blue
end of the spectrum. What colour the light actually is depends
on what the original frequency of emitted radiation was. – 
Kitchi Dec 11 '12 at 13:31 @Kitchi: So I guess an ultraviolet
source would be shifted away from the blue, yet be erroneously
called blueshifted. –  dotancohen Dec 11 '12 at 14:53 It may be
a good idea to tre