You just substitute what ever fabrics you like. Thats what I do. I like to follow mystery quilts but use my own idea for fabrics, can't ever follow a pattern exactly. Sometimes it is an improvement and sometimes you end up with a donation quilt, someone will think it is wonderful! Just as long as you go with background and med and dark, but I have even gone with dark background and light/med. It can come out totally different. My friend and I did a mystery recently and she swithed her dark and medium and I did the opposite and both were just beautiful!