The difference between rods and cones can explain why we can see colors clearly in a bright environment, but we can't distinguish colors in a dim environment. Under the bright environment, cones are working, and they detect colors well, while under the dim environment, rods are working, and they cannot perceive color.
The fact that one has no color vision in dark really surprised me!
Dogs only have two types of cones so they see a more limited range of colors than humans, but they (and many other mammals) have more rods than we do so they see better at night!
I was in another class last semester and worked on a real-time filtering app for color-blind people. There were two types (among 5 total) of color-blindness related to rods and cones:
Rod monochromacy (RM): People with RM have no cone function and no normal rod function. This is called total color blindness, and people with this condition can see only shades of grey.
Cone monochromacy (CM): People with CM have only one functioning types of cones (out of 3, which means there are 3 subtypes of CM). They can see color patterns just fine with sufficient lighting, but can't distinguish between some hues.