Elves and gnomes ought to be colorblind. Unless their low-light vision is magical, which the rules don't indicate.
I'd say orcs and dwarves, too, except that darkvision basically has to be magical. No animal on earth can see in absolute darkness. Animals that can see in the dark are just very efficient with the available light.
One of the ways to maximize this efficiency is by having lots of rod cells and few cone cells. Cones register color, but need more light to function. Rods only register greyscale, but don't need as much light. Since there's a limited amount of real estate in an eye, a creature can either be good at seeing color or good at seeing in the dark.
Maybe I'm missing something. Or maybe elves and gnomes just have extra-dimensional spaces inside their eyes.