Set background opacity
Bring the opacity down so the background hints at the image rather than competing with the photos on top of it. That also lets your background color show through.
Starts at 40:31 in the full tutorialWatch on YouTube
More in Backgrounds, borders & gaps
See all 10Add a background image to a spread40:18Apply a background to every spread40:41Change the project background color46:27Add borders around your photos46:46Set the gap between photos46:00Remove the gap at the book gutter43:07Fill an empty placeholder with a color or gradient0:47Pick a color with the eyedropper1:40Hide the book gutter indicator45:43