I'd use solid black for the sashing with pure white cornerstones, the same width as the white crosses in the blocks. The cornerstones would connect the blocks forming a lattice all over the quilt, and the black would accent the blocks so you would then get a secondary pattern. Be sure to put the sashing around the outside of the blocks as well as between them, before adding borders. For borders I would use a black and white print to draw the eye outward... then finish with black binding. Black and white is so classic it does not need to have any color added and will match with any color accessories. If it were mine, I'd stick with just black and white, then if I wanted a pop of color I'd add a red pillow or such. That's my choice, but you can't go wrong however you do it. Great job.