Oh -- another thought on random and improv. It's those "off" blocks that give the completed quilt its spark. Everything matchy and coordinated and planned ends up looking very canned and predictable, while a little dissonance keeps your eyes coming back.
If you're having a hard time dealing with the clash effect, work with smaller pieces. The quilt in my siggie has a lot of really "off" fabrics side by side, but because the individual pieces are small and all is contained in rows, with lots of white and black to rest the eye, it ends up looking luminous and interesting -- far more so than if I had lined up each color range in a pattern or by ascending value.
RST