Prime the walls with white primer. You may need two or three coats. Then when you get the bedding, use the color wheel to find the undertone. The reflections of the gray will not confuse your choices. Or just take a pillowcase to the paint store and have them custom mix an off white to match the background in the print. Buy a small test can first.

It’s really impossible for us to accurately assess the true color on our screens. The color wheel doesn’t help either because we are not in your space to see how your lighting affects whatever color you might choose! In other words we can’t trust what we are seeing is what is actually what you are seeing! Bring home some color chips first; see how they look in the room. Narrow your search then get some samples. Do a sample board( larger the better) and go from there.