How can frequency be constant during refraction? When entering from a rarer to a denser medium, the speed of light decreases.I know that the frequency remains constant.But if frequency is cycles/sec then doesn't that mean more speed will lead to more cycles/sec? and if the wavelength changes, should i see a different color all together? I'm not familiar with the 'complicated math' so is there another way to understand?
 A: The perception of 'colour' is loosely based on a transfer of energy from photons to photoreceptive proteins in the retina. This suggests that frequency is responsible for perception of colour since the energy of a photon is directly proportional to frequency.
The frequency does not change because the energy does not change.
This would imply that there is no change in colour with refractive index, even though the speed and wavelength of the light wave changes. 
A: Put simply the energy of a photon is given by E=hf where h is Plancks constant and f is the frequency. The photon does not transfer energy to the medium so therefore E remains constant and so must f.
A: Light consists of photons. In the period between the photon's emission and its absorption photons are indivisible units.
In every media in which the photon is not absorbed, the photon is subject to the influence of the medium. The influence is carried out mainly by the interaction between the electric field of the photon and the electrons of the medium. In vacuum, the largest distance is covered during one oscillation of the electric and the magnetic component of the photon. In a medium as well as in electromagnetic fields, these vibrations are slowed down. However, the energy content of the photon remains unchanged and any color sensor - even the human eye - stated inside the medium the same color as outside the medium.
