I want to make my nephew a quilt for college, and thought of using a jelly roll, but then thought of just buying cuts of fabric if can't find colors I like. But, he wants a blue quilt. I know I can get various SHADES of blue, but also know it will be more interesting if it has other colors to contrast with. Is there a general "rule" how much OTHER to have? If I need 40 strips, then should 20% (* strips) be another color? How do you decide how much OTHER to put in a quilt? I have never done a scrappy before.