Large areas of a different color are best done by only lapping the seams about 1/4" instead of covering over covering. Depending on your layout and if the surface is solid or hollow, this isn't always possible though. I don't believe the Windex route will work on anything but trim sheets that are sticky backed because even if you wait overnight for it to dry, as soon as you put the heat to it you'll get bubbles. If you have to put covering over covering you need to set your iron as low as it will go.