Are different colours/frequencies of light travelling along each other or they are superimposed? When white light is traveling, do its components travel alongside each other without affecting one another?
How is that possible, if they are propagating in same medium at same time at same position, how come they not superimpose and travel as single wave?
(I feel they don't superimpose since prism is able to split them apart)
 A: Photons with any amount of energy/frequencies can all propagate together without affecting one another. Even billions of identical photons, coherently radiating from a common source, propagate as individual photons without affecting each other.
A: With sound waves, there is a medium. If different frequencies travel together, then they excite the medium together, a superposition is created. However, our senses are able to pick out individual frequencies.
This is different with EM radiation. Photons, regardless of the source, almost never influence each other. They do not need a medium. And they are invariable units from emission to absorption.
The case of superposition, on the other hand, does occur at the receiver. Take two radio waves. When they hit the receiver, both will cause the periodic displacement of electrons on the antenna rod. Depending on the direction in which this occurs, there will be an amplification or a weakening. And ideally, even extinction.
A: Optical instruments like prisms and lenses didn't bring about a crisis in physics the way blackbody radiation or the photoelectric effect did. There were many scientists before the 1900s who understood the dispersion properties of transparent materials very well. When it comes to mathematical concepts like superposition, the physicist should not ask whether it literally occurs in nature (the answer to that is always no... every idealized phenomenon has higher order corrections). Instead, she should ask if it's a good model. And superposition for light waves of differing frequency is a good model.
If a device transmits radio waves where the amplitude, frequency or phase is modulated (the basis for all wireless communications) then it is true to a high degree of accuracy that it is sending out waves which are superpositions of more basic ones. The statement that it is really sending out photons which create the illusion of superposition seems to be on par with the claim that waves are illusory in water as well. After all, any microscopic description of interacting water molecules has no intrinsic notion of a wave.
Yes, photons improve on these old models in many ways but the linearity of Maxwell's equations is a consequence of the fact that photons interact negligibly with each other. Viewing this ability to add two waves as a hypothetical scenario which never needs to be considered in view of photons is a bad idea. It's only possible to talk about photons that come out of a source and go into a detector if they are superpositions of single frequency photons which are necessarily delocalized. Exciting the electromagnetic field with quanta which have no probability of occupying the same position is trying to have our cake and eat it too.
