Well, I have to say that I buy what pleases my eyes. Having said that, I also sew together what pleases my eyes. If you are worried that something you put together will not look good, I wonder if getting a color wheel would help a bit. It can tell what is a good contrast. Maybe for your first venture outside the comfort zone, you could keep it to about 3 different fabrics, that are not too "busy", then go from there.