I can't change my messaging app background image back to default

[AC Question]

I have an HTC m9 with marshmallow. I changed my default messaging apps background image, but I want to change it back to the default. In the setting there is a setting that says it reverts to default the background image and bubble colors. It changes the bubbles back, but not the background. Any ideas?

 

[B. Diddy]

Moved to the M9 forum.