I think some other color than white for sashing. I think that sashing would definitely define the blocks. However, your quilt, your choice, I like it both ways, but I personally prefer sashing. I think black would set it off. If you have some black bias tape, lay it along the blocks before you buy black fab. and see how you like that. When I'm not sure, I try colored bias tape to see what I might like, then purchase fabric saves $$$. I use my digital camera when I am trying to decide. I always take pics. of different set ups then I can tell what I want and remember how I laid the blocks out. I have found that viewing it through a camera eye is a big help to me.You might try laying the blocks so that all of the same colored blocks are going in a diagonal directions making a line down the quilt without sashing and see how that looks. gives you a different design. Also make them form a diamond with the colors. Just a thought.