electromagnetic radiation - Dependence of Color of Light on Wavelength?

Recently i saw a question here which asked "what does the color of light depend on as we percieve it?".Now some members answered that if you see an object from any other medium it appears the same colour as in air.But we are forgetting that light passes through aqueous humor and vitreous humor or some fluids in the eye which changes the wavelength to some "constant" (say).Now this constant will be same as in air or water.basically the fluids act like filter.so how can we explicitly say that color of light depends on frequency?

Answer

The short answer is that the perceived color depends on the impacting photon energy, which is unaffected by changes of refractive index.

A much longer and yet still incomplete answer would be that the exact color "perceived" (i.e. at the consciousness level) is in large part an illusion, depending on an awful lot of factors:

• biological, e.g.
  
  
  
  • the exact composition and distribution of the colour receptors in the retina's rods, leading both to dischromatopsy (colour blindness or wrong perception of colour) and tetrachromacy,
  
  
  • the exact composition of the opsine molecules present in the retina's receptor, which is not the same in all human beings, and also affects relative color perception (i.e., two people may agree that a given frequency is apple green, and yet disagree that a different frequency is deep red).
  
  
  • receptor density and efficiency (e.g. phosphodiesterase-6 inhibitors cause cyanopsia, a blueshift in the perceived colours, by keeping blue opsine receptors overstimulable),
  
  
  • blood perfusion of the retina (which mostly influences light perception, but colour too),
  
  
  
  



• 
  

  perceptual, e.g.

  
  
  
  
  • by mixing two colours I may be able to make you perceive a third colour, whose frequency is nowhere near the light actually arriving into your eyes,
  
  
  • by rapidly alternating several colours I can do the same (see Newton's Color Wheel)
  
  
  • by juxtaposing two different colours I can do even worse.
  
  
  
  


• 
  

  psychological, e.g.

  
  
  
  
  
  • some people may see (rather "perceive") colours that are not really there at all (it was a famous quirk of the Nobel Prize Richard P. Feynman); the same effect may be obtained with any one of several psychotropic drugs;
  
  
  • some people may perceive different shades of colour depending on mood (the reverse of the common belief that color affects mood)
  
  
  • it has been suggested that color perception is also culturally based, so that Homer actually did see the wine-dark sea, and some populations see shades of green that other populations are unable to tell apart.