You're going to make that box the background color. Click on the box in the toolbar that
represents the background color. The picker tool will be active, place it on the blurred box and
click, then click the 'OK' button. That blurred box color is now the background color. Can't find
the toolbar? Click on {Window}, if there's a checkmark next to 'Tools', then the toolbar is
somewhere underneath an open image. If there's no checkmark, then just click on {Window - Toobar}
and the toolbar will appear. I frequently have half a dozen images open and no clue where the
Toolbar is, so I click on the (checkmarked) {Window - Tools} to uncheck it, then click it again to
open the toolbar and it will appear on top of an image.