From what i think i understand about the way the eye works, we have cells which can identify either red, blue or green light, which i guess corresponds to a certain wavelength (475nm, 510nm, 650nm), yet yellow light, for example, has a wavelength of 570nm. Is this picked up only partially by red and green receptors? If this is the case, technology using 3 colours of pixels in screens must be perfectly adapted to human eyes, yet a new type of television has been released with a yellow pixel as well. Would that offer any advantage to colour perception, or is it just smoke and mirrors?

During a recent lecture on the use of confocal microscopes, we were told that red light penetrates further into tissue than blue and green light.   This was demonstrated by the fact that a red laser is still visible when shone through a finger, but a green one isn’t.   This contradicts the loss of red light that is observed as you descend underwater; everything appears blue at depth when scuba diving.   Why is this?

I am exploring the properties of waves when traveling thorough a transparent medium. I observed that when white light is shone through a prism the blue light refracts more than the red light in the spectrum. This is due to the interaction between the blue light and the molecules within that medium. 

I wish to know if anyone can give me more details the nature of this interaction.

A more through explanation as to why wavelength of the light effects the speed through a medium would be appreciated and any relevant laws or theories as this is a mystery to me.