Welcome from Texas. I use a lot of white in my quilt tops, and I use white Warm and Natural batting. I have never had a problem with the backing showing through. An orange should work really well for the back, a lighter orange if you are really concerned about it. I also use white backings often, and that has never been a problem either. I don't drag my quilts around on the floor like a kid would, so they don't get dirty or anything.
Your quilt top is beautiful, by the way. You have to be proud of it!!!
Dina