enable monochrome panel for transparent panels

-- in dynamic background it might be important for
the user to increase the contrast because the textColor
from plasma theme and the background might not provide
readable contrast. This feature adds this by giving
to the user the choice to have as monochrome layout
when the panel is transparent to theme.backgroundColor

containment/package/contents/config/main.xml

@@ -75,6 +75,9 @@
     <entry name="solidBackgroundForMaximized" type="Bool">
       <default>false</default>
     </entry>
+    <entry name="colorizeTransparentPanels" type="Bool">
+      <default>false</default>
+    </entry>
     <entry name="splitterPosition" type="Int">
       <default>-1</default>
     </entry>

containment/package/contents/ui/main.qml

@@ -21,6 +21,7 @@
 import QtQuick 2.1
 import QtQuick.Layouts 1.1
 import QtQuick.Window 2.2
+import QtGraphicalEffects 1.0
 
 import org.kde.plasma.core 2.0 as PlasmaCore
 import org.kde.plasma.components 2.0 as PlasmaComponents
@@ -86,12 +87,14 @@ DragDrop.DropArea {
     property bool editMode: editModeVisual.inEditMode
     property bool forceSolidPanel:  plasmoid.configuration.solidBackgroundForMaximized && dock && dock.visibility
                                     && Latte.WindowSystem.compositingActive
-                                    &&(dock.visibility.existsWindowMaximized || dock.visibility.existsWindowSnapped)
+                                    &&(dock.visibility.existsWindowMaximized || dock.visibility.existsWindowSnapped || hasExpandedApplet)
     property bool forceTransparentPanel: root.backgroundOnlyOnMaximized
                                          && !(dock.visibility.existsWindowMaximized || dock.visibility.existsWindowSnapped)
                                          && Latte.WindowSystem.compositingActive
                                          && !(hasExpandedApplet && zoomFactor===1 && plasmoid.configuration.panelSize===100)
 
+    property bool forceColorizer: plasmoid.configuration.colorizeTransparentPanels
+
     readonly property bool hasExpandedApplet: plasmoid.applets.some(function (item) {
         return (item.status >= PlasmaCore.Types.NeedsAttentionStatus && item.pluginName !== root.plasmoidName
                 && item.status !== PlasmaCore.Types.HiddenStatus);
@@ -1622,7 +1625,35 @@ DragDrop.DropArea {
 
     VisibilityManager{ id: visibilityManager }
 
-    LayoutsContainer { id: layoutsContainer }
+    LayoutsContainer {
+        id: layoutsContainer
+        opacity: !layoutsColorizer.isShown ? 1 : 0
+
+        Behavior on opacity {
+            NumberAnimation {
+                duration: 0.8 * root.animationTime
+                easing.type: Easing.OutCubic
+            }
+        }
+    }
+
+    Loader{
+        id: layoutsColorizer
+        anchors.fill: layoutsContainer
+        active: forceColorizer
+        z: layoutsContainer.z + 1
+
+        property bool isShown: active && !forceSolidPanel && plasmoid.configuration.solidBackgroundForMaximized && !root.editMode
+
+        sourceComponent: ColorOverlay {
+            source: layoutsContainer
+            opacity: layoutsColorizer.isShown ? 1 : 0
+
+            color: theme.backgroundColor
+        }
+    }
+
+
 
     ///////////////END UI elements
 

shell/package/contents/configuration/TweaksConfig.qml

@@ -122,6 +122,20 @@ PlasmaComponents.Page {
                 }
             }
 
+            PlasmaComponents.CheckBox {
+                id: colorizeTransparentPanelsChk
+                Layout.leftMargin: units.smallSpacing * 2
+                Layout.maximumWidth: dialog.maxWidth - 3*units.smallSpacing
+                text: i18n("Background color for contents when panel is transparent")
+                checked: plasmoid.configuration.colorizeTransparentPanels
+                tooltip: i18n("The panel contents are colorized in order to improve contrast \nwith the underlying desktop background when the panel is transparent")
+                style: LatteCheckBoxStyle{}
+
+                onClicked: {
+                    plasmoid.configuration.colorizeTransparentPanels = checked;
+                }
+            }
+
             PlasmaComponents.CheckBox {
                 id: hideShadowsOnMaximizedChk
                 Layout.leftMargin: units.smallSpacing * 2