People want to see the wood. That means more transparent stains. That requires organic dyes. That means they are a bit more sensitive to light (not just UV by the way, photosensitivity can be to all parts of the light spectrum, and dyes will fade in artificial light, it's about the photons given off, not necessarily UV photons).
Keep them cased when not in use and they rarely fade at all. But hang them on the wall in a room with a window, or with electric lights, and they'll fade over time. How much depends on the intensity of the light and the colors themselves, as some colors have greater photosensitivity than others.