Yes, you could say "will be fading" if you want to stress the process. If you want to stress the result, I would say: If you print that photo, the colors will fade over time/ over the years. Or, you could say: will start to fade.
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AnonymousI want toShadows don't fade away with time, but colors do. Why not just:exprenseexpress how color or shadows will fade away withthetime...