Here is what I would do if I were adding borders: Since the outside edge is all darker fabrics, I would add a narrow border of the yellow to frame the quilt. (I would not use the light blue, since it is more of a background fabric in the pattern and does not need to be pulled out.) Then do a wider border, whatever width you need to make the finished quilt the size you want, of one of the darker fabrics in the quilt. The purple is fine or even one of the dark blues. I personally like borders as a frame for quilts and I'm often ready to quit piecing blocks by the time I get to this stage in the process.