some companies are much better at providing 'colorfast' fabrics- some still seem to use (lesser quality) materials *fibers & dyes*
so, testing is always a good idea, and paying attention to who manufactured the fabrics will help you choose fabrics that do not fade away to something much less than what you saw on the bolt. I know people have to watch their budgets, and look for bargains- but sometimes the cost in the long run winds up being much more.