You can have contrast in a quilt using lights and darks, or by using different colors. For instance, if you have a lot of medium and dark blues, and also a lot of medium and dark reds, you can use those in much the same way as using lights and darks. Or you can always make string quilts, which often have no light/dark contrast at all and rely on the wild assortment of colors to make them beautiful. Some other patterns, such as "just" squares will work too, and you can throw in a little muslin sashing if you want to give it a more planned appearance.