There are certain colors that always appeal to me as do Roses in fabric. I rarely, purchase backing until the project is done.
There are times when I will purchase a main fabric, hold it for awhile, then start hunting for accent fabrics and the pattern to build my project.
Right now I am looking at Moda's Sweet Sixteen in pink or yellow.
http://www.unitednotions.com/fcc_Sweet_Sixteen.pdf