dbus-send --session --dest=org.kde.plasmashell --type=method_call /PlasmaShell org.kde.PlasmaShell.evaluateScript 'string:
var Desktops = desktops();
for (i=0; i < Desktops.length; i++) {
        d = Desktops[i];
        d.wallpaperPlugin = "org.kde.color";
        d.currentConfigGroup = Array("Wallpaper", "org.kde.color", "General");
        d.writeConfig("Color", "93,93,93");
}'