So sorry to hear that they faded. What brand of pastels did you use? I've heard of them going dark because of spray.... what spray did you use? I don't use any fixatives, which for me is fine as they aren't readily available here.
When framing the pastels always try to use a non reflective UV protective glass. Also if the paintings were hung where direct sun, or even in a brightly sunlit room they can fade just as w/c will.
