I used King Tut for both the brown and the blue threads. One thing about King Tut is that it is a very subtle color change, and that is why I think it did well... you can still notice the spine lines... which are important in the overall look of a feather. I used an Isacord polyester for the "fill-in" stitching in the center... it was really HARD to see! I won't be doing that again anytime soon, although I liked how they really did 'disappear' into the background fabric.
material I really LIKE... then it's different for me! I try harder! Kind of just like a real dress-rehearsal does for actors! It builds your skills, while giving you something tangible to show for your best effort, and it also serves a valuable role in that you can have a piece to judge where you may you need to improve. And those fledgling skills ... turn into REAL SKILLS! Yay!
And don't forgetthe "hidden advantage" of using a straight stitch foot!