White is my favorite accent color it can just pop the other fabrics. I do not prewash any of my fabrics but I only use QS fabrics. The LQS owner told me she has only had 1 fabric run in all her years of business. If you use a lesser expensive fabric it should be pre washed to be sure.
Nothing I have made with whites has ever faded or run. I wash all my quilts especially baby quilts after they are made and quilted.