I like the idea of a narrow flange (like a 1" strip folded in half and sewn on with the fold to the center of the quilt top), then maybe a narrow border of the background color, and a wider border of one of the favortie colors in the blocks. I would not do any more blocks in the border. Like another lady said, your blocks are so nice in the top that you don't want to take away from those. And it would give you a space to do some neat quilting in that border. I would do that little flange in a darker color but not black....maybe navy blue or a darker green, or maybe even a brown. It will be a beautiful quilt. Hope to see it when it is done!