The way we see colour is via a photochemical reaction in the eye which passes information to the brain. The colour sensitive cells in the eye are called the "cones", and we have 3 types of cone cells -short, medium and long wavelength. What we perceive as colour is actually a synthesis of the the information passed to the brain by these cone cells in the cortex and associated areas in the brain.
This is how it works across all humans, except those with genetic/hereditary problems or damage to the macula, which is why we have a common agreement on what synthesis hue constitutes red, as opposed to scarlet, for instance.
http://en.wikipedia.org/wiki/Color_vision
Birds have 4 types of colour receptor cells, so the range of their colour and hue distinction is more sophisticated than humans, and the dominant "colour" that their cone cells detect is skewed toward the UV portion of the light spectrum, rather than visible light spectrum as humans do. Consequently, Birds will see the colour of a rose petal, say in a different way to humans. Insects too see primarily in the UV verging into the blue/green visible light spectrum.
And a plants leaf/flower looks much different when viewed in UV light.
http://www.naturfotograf.com/index2.html