I would play around with several solid colors taken from the fabrics-- maybe 5 different colors/shades, distributed around the edges in such a way that the color makes the turn at the corners . I might even piece some interesting very thin strips of the striped fabrics into the border, maybe making an arrow effect chasing around the perimeter. And after I tried out those awesome ideas, I would probably decide to go with no border and I'd use the discarded border concepts to make coordinating throw pillows.