Your blocks are really pretty. I would love to see all 60.
It would depend on the "look" you are going for as to the color for sashing. Your stars and backgrounds do not seem to have a lot of contrast, so the quilt is a very soft, subtle palate. To continue that look I would go with a soft green like in the star #2. Or maybe a pink. But the best way to decide is to lay out some fabric and then lay your blocks on top, leaving them far enough apart so that the "sashing" shows. Take the blocks with you to a quilt shop and audition fabric. They LOVE it when you come in and ask for opinions--they live for that stuff.
Oh, and let us know what fabric you decide.