Is it a Cayuga duck egg? I've heard of duck eggs turning all different colors during incubation. I don't have any experience hatching duck eggs, though.
If you don't get enough answers here, you could try posting in the Incubation Forum or the Duck Forum. Keep us posted and I wish the best for your hatch!
Thanks for joining and welcome to BackYard Chickens!
But as a practical matter, if it is due to hatch tomorrow and is showing movement, I would treat it like any other egg that is due to hatch at that time, and see what happens.