IMHO, I would add a very narrow border of the dark color of the hummingbird fabric background. The dark narrow border will frame the quilt and give it a stopping place. Then a narrow border of the bightest pink fabric color then a wider border of the brightest purple fabric color. or vice versa. The pale colors of the solids of the rail fence block will get lost in a border. I would end with the dark fabric color as the binding. It's a very striking quilt!