Are you saying that your sashing will be 5 inches wide? that is rather wide for sashing, generally sashing is only 1-2inches wide.
if you are planning on doing 5in wide sashing, then I would do 1.5in yellow, 2in main color, 1.5in yellow....Like a strip set, the main color would be whatever you decide is the focus color for you. I would then do a 2in border in yellow then a 5in border in the main color to tie everything together.