Hypothetically, if our sun was yellow would we still see "white" colours? Hypothetically,if our sun was yellow would we still be able to see white colour on objects like snow,cotton etc.? Would we have the phenomenon of rainbow?
Every "normal" star, produces a more or less "black-body" spectrum, at some temperature (more-or-less because there are brighter and darker lines caused by specific elements in the upper layers of the star), so there will always be a range of colours of light (or electromagnetic radiation at least) in its light, which can be spread to give a rainbow. 

A white object (like ice crystals, or bleached cotton) reflects all colours of light more or less equally (over some range of wavelengths of interest, anyway). 

So, if the Sun suddenly cooled, so that it was emitting a 5000K black body spectrum instead of its current 6000K, with more red light and less blue light, that change would be reflected in the light reflected from a white object, which would look more yellow or orange to our eyes. 



There are a couple of caveats though:


As @badjohn pointed out in a simultaneous answer, our brain processes visual information in odd ways. If the colour of sunlight changed, the brain might try and compensate for the overall shift and you might see everything more as you expect it, and less as it now is.
We evolved to perceive sunlight as white. If we had evolved around a cooler star, we would probably perceive a different colour as white.