If she skipped the sashing, that would mean more blocks were needed. Color is such a personal choice. I would love turquoise or red. But most importantly, what would your recipient like? How wonderful that they would have the opportunity to participate in the creating of their quilt. What colors are in their bedroom? Luckily black and white can pretty much go with anything. The color(s) you choose though will have a dramatic impact on the final look and mood of the quilt so do as others have suggested and try several layouts of blocks on different fabrics, even once you have decided color! If you have a design board that would help tremendously.