Blank or solid or gradient background option for monitors

[AJCxZ0]

An option to set no wallpaper, i.e.

org.gnome.desktop.background.picture-uri='""'
 org.gnome.desktop.background.picture-uri-dark='""'

or a solid color, e.g.

org.gnome.desktop.background.color-shading-type='solid'
org.gnome.desktop.background.primary-color '#444444'

or a gradient, e.g.

org.gnome.desktop.background.color-shading-type='vertical'
org.gnome.desktop.background.primary-color '#444444'
org.gnome.desktop.background.secondary-color '#666666'

for each monitor in the Per-Monitor Configuration.