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Just a tad to add to Chris' excellent post on night vision, from a reformed physiologist. The reason that cone photoreceptors give rise to colour vision is that there are three populations of them, each maximally sensitive to a different wavelength of light. The brain sorts out colour by comparing the relative activity of each population for each part of the visual field. The rod cells are much more sensitive, but there is only one population of them, so the brain cannot work out colour from their signal - so night vision is monochrome.Only when there is enough light to stimulate the less sensitive cones (eg when viewing planets) will you see colour.
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