I think keep it simple. Perhaps evenly spaced lines or waves. So you won't distract from the feather and maybe use a white thread to tie it all together.
However when I am really stuck I make mock up. For you cut a block as designed with the blue and white (no feathers) and concentrate on doing something with the blue part. Stand back and imagine it with the feathers in place. You will see what scale is right, what feeling is right and what thread color to use. Maybe waves, or leaves on a vine or simple straight lines on a diagonal.