Omigosh is correct - that quilt is Gorgeous!!!
IMHO - the simpler the better for the border. A small colored border to frame and a light (maybe the background) on the outside. Although I love piano pieced borders and have used them several times, I think that it would detract from the visual impact of the blocks.
If I did not do a simple border, I would try to bring some part of the design of the block outside to the border. Here is one I did. If you wanted a touch of color in the outer border you could float small squares of color in the background or in a wider border of background float a small nine patch (the size of the one on them inside your setting squares) to bring color and continuity.
Good luck - it is always so hard - but when something strikes you - you will know!!