While I suggested the attic windows before, the more I looked at it and thought about it, I got cold feet on that!!
There's enough going on in the fabric, that I'm not sure I'd want to put much with it, re colour or block design. To me, they'd end up competing and I'd never be happy. So .... Keep It Real Simple!
One idea ..... a large centre of the print, then a dark navy or black border, 1-1/2" or so ..... and a strip of the print ... another dark border, a little wider than the 1st one .... and then a 6-8" border of the print. I might even go with a 3rd black border (again, not overly wide as a final border and skip the print border.