What a fun project you're planning! I've made a Santa quilt in all red, using perle cotton
in a variegated red. I layer my blocks with flannel to prevent the under-stitching from
showing through and I like the extra puffy-ness it gives my embroidery. Wash the flannel
a couple times in HOT water and HOT dryer to be sure it has shrunk. I've also made
several other quilts with embroidered blocks and they have been laundered and held up
well. The advice to soak the thread first is a great one and if you have some Retayne
I'd put some in the water to be sure the thread color is set. Trace your design with a
washable Crayola marker or a pencil made for use on fabric so it will wash out
(Fons and Porter makes one). Good luck and happy embroidering!!