Oh, I totally would not use the white sashing with such deeply pigmented colors. It would just break up the whole look of the quilt. Since you are using such color saturated colors, if you really want to add a sash, I'd go a step further with the depth of color, and use something like deep purple, no pattern. The purple would really set off your other colors nicely. Just don't make the sash too wide. Just a narrow sash, just enough to "square up" your blocks, and I think you'd be happy with that.