If all the blocks had solid black in them then I might go with the black because the other color in the pinwheel would be set off and it would look like those pin wheels floating and twirling. I notice that you have some solid black and some with confetti colors on black. If you use black sashing in this case I think it might look disjointed with some pinwheels having 4 blades floating and some pinwheels having 8 blades distinct. A different color sashing would also set the blocks apart where black will give the appearance of the whole quilt being the block.