I'm using the craft template. The background is green. How do I change the background on all the pages to white? The unlock option is not highlighted

Backgrounds are either images or colored boxes. To change a background, you need to select it in the layout. In the case of Craft, it is locked. You will notice the "x" at each corner of the layout background once you click on it. If they don't show up it's because you didn't select the object properly. Just click in one of the corners. To unlock, click on Arrange -> unlock. Simply delete the background object and you can then insert a new one. You could also just modify the object color properties after it is unlocked.