cones come in three types: R, G and B
red cones respond primarily to frequencies in the lower part of the range of vision
green respond primarily to middle frequencies
blue respond primarily to the higher frequencies
subtleties in color comes from our brains processing the extent of stimulation of each type of cone by a particular frequency (more commonly a narrow band of frequencies).
our eyes have about 45% R, 45% G and 10% B cones
so rods and cones act as a sort of 'radio' antenna for these frequencies
the incident light in the proper frequency range cause electrical impulses to be sent by the rods and cones through the optic nerves to our brains for multilevel processing
other animals have been shown to have receptors outside the range of human vision
bees, for instance, are believed to be able to perceive well into the UV range
dogs seem to have only rods and so are believed to see only in 'black & white'