... when another Layer is active?

I have a single element (a large white rectangle) defined on the Mouse Off layer. Previously, I've designed all other layers to either coordinate with or overlay the Mouse Off elements. But now I'd like for the large rectangle to disappear (become invisible) when I call up other layers. It will greatly simplify the site's design.

Is there a feature for this? Or do I have to move the rectangle and its associated Mouse Off elements to a Layer 1? (IOW, leave the Mouse Off layer to have only the site header.) If so, how do I cause Layer 1 to always be active when the page first comes up?

Thanks in advance for any suggestions.