# List available keys and their values
# gsettings list-recursively org.gnome.desktop.background

# List valid values for a key, e.g. color-shading-type
# gsettings range org.gnome.desktop.background color-shading-type

# Now, really do it
gsettings set org.gnome.desktop.background color-shading-type vertical
gsettings set org.gnome.desktop.background primary-color "#000000"
gsettings set org.gnome.desktop.background secondary-color "#ffffff"
gsettings set org.gnome.desktop.background picture-uri ""