The photo may not do it justice, but in person the red is so much less harsh than the black. It needed to be a much narrower border (1" or less) and then the black frame on the outside edge really sets it off. The black will be no larger than 1.5". We tried the blocks without the sashing, but my sisters liked it this way much better, and I agree. You can see the details of the blocks, this way. In person, the red/pink border is so much calmer and allows the eye to flow from block to block. The black didn't. We realized that when we tried the red one more time with the narrower frame (thank you, Terrie!!!) Adding the black border provides a stop, and it needs to be fairly thin. However, looking at the picture, I am definitely going to try it without the black once the top is pieced.
This will be part of the backing. The rest will be pieced.