Groton of Willows

I was just looking up how to do it when I found this conversation. The method I use is to open my document in Affinity Photo which allows me to create a fill layer which I can then put at the bottom of all the layers. It would be nice to have that facility in Publisher though, It is just as well that I have Photo as well as Publisher. When both are open on my Mac desktop it is easy to flick backwards and forwards.