Is this the one from Craftsy, where each block is a different pattern? I think black sashing can help a lot to bring a quilt like this together. The width of the sashing depends somewhat on the size of the blocks and the finished size you want for the quilt. I like a relatively thin sashing in black; it is enough to set off the colors but does not overtake the blocks. If the finished blocks are 12", I would probably use a 2" wide finished sashing throughout and add a wider border in black.