Warning. This is real world physics and visual perception. I have no idea about how D&D canon describes darkvision. If you want a fantasy answer, just skip over this one.
If darkvision works in another band of the electromagnetic spectrum, that should probably be in the far infrared range, where room temperature objects are emissive, that is they emit light. This would allow for perceiving contrast in both temperature differentials, and different reflectivities of objects. However, the luminance values should probably be much different than what we see with the visible spectrum, so contrast levels will also be very different. It is possible to lose some details while some things that are lost to us will be easily visible. And transparency will also work differently. Some transparent things may be opaque down there while some other normally opaque things will be transparent.
It is also possible to discern color at that range, but those colors will also be very different than our colors, and no information about our colors will be available. So it is logical to say that while darkvision enabled characters see some sort of color information, that color has no correlation to our visible spectrum color.
In other words, it will be a different and magnificent world.
If darkvision works like our own real-world darkvision, which is just light-sensitive and color-insensitive rod cells in the retina, then it needs light, however little that may be. We have a low number of rod cells so our darkvision isn't very good compared to say, cats or owls. They have a high number of rod cells in their eyes, so they can get by easily in starlight. Pitch darkness, which is really hard to find(magic?) would disable such darkvision.
Rod cells have a sensitivity curve that peaks at a single color. For us, that happens to be the color blue. At night, blue appears brighter and red things appear darker than all others as our rods are completely insensitive to red. So while there is no real color data in real-world darkvision, it is possible to deduce color based on luminance, but it is also possible to be mistaken about color in the dark.
Both kinds of darkvision would be overwhelmed in the presence of sunlight, so creatures possessing darkvision would either be nocturnal like owls, or have dual vision systems like us humans.