If all of your colored strips are the same width, then the solution is this. After you sew the sashing to the first piece, turn it over. On the wrong side, using a pencil and ruler, mark each seam allowance across to the other side of the sashing. Pin the next piece to that sashing, matching each seam on the new piece to each pencil mark on the sashing. This will force you to ease either the sashing or stripped piece as you sew to get the two to match.
That will pretty much solve the problem.
Edit: Another thing that will help is if you measure the colored sections first, similar to how you would measure a quilt for adding a border. Measure all 3, average the measurements, and cut the sashing strips to that length before adding the first sashing strip.
p.s. I really like the quilt and may steal that idea!!!
Last edited by Prism99; 03-10-2012 at 09:45 PM.