Quality windows will not have that issue. Cheap builder grade very well may.

Everything fades. White typically shows fading less than black. Extreme weather, Perception and time are the biggest enemies .

You didn't mention whether you have wood windows, vinyl windows or aluminum windows. But regardless, all of them will fade at some point and depending on the amount of light exposure they fade sooner or later. Other colors fade as well but a grey color for example is not that visible as black. So if you can scale down to medium grey for example, you should not have a visible problem in the future.

There are ratings (AAMA)applied to painted aluminum wood clad (2603-04-05) and fiberglass coated (623-24-25) windows. The higher the number, the better. I don't believe there is an AAMA rating on painted vinyl windows, only the manufacturer's warranty. Ten years is the best I have seen on vinyl but it is always to the extent of fading (as stated previously by others). the most extensive fading is usually product with the most sun exposure. Look for this as part of the warranty and go from there. Hope this helps.