Fix Rectangles that always show as white regardless of the theme

plugins/LayerView/LayerView.qml

@@ -41,8 +41,9 @@ Item
             width: valueLabel.width + UM.Theme.getSize("default_margin").width
             Behavior on height { NumberAnimation { duration: 50; } }
 
-            border.width: UM.Theme.getSize("default_lining").width;
-            border.color: UM.Theme.getColor("slider_groove_border");
+            border.width: UM.Theme.getSize("default_lining").width
+            border.color: UM.Theme.getColor("slider_groove_border")
+            color: UM.Theme.getColor("tool_panel_background")
 
             visible: UM.LayerView.getLayerActivity && Printer.getPlatformActivity ? true : false
 

resources/qml/MonitorButton.qml

@@ -15,12 +15,13 @@ Rectangle
     id: base;
     UM.I18nCatalog { id: catalog; name:"cura"}
 
+    color: "transparent"
+
     property bool printerConnected: Cura.MachineManager.printerOutputDevices.length != 0
     property bool printerAcceptsCommands: printerConnected && Cura.MachineManager.printerOutputDevices[0].acceptsCommands
     property real progress: printerConnected ? Cura.MachineManager.printerOutputDevices[0].progress : 0
     property int backendState: UM.Backend.state
 
-
     property bool showProgress: {
         // determine if we need to show the progress bar + percentage
         if(!printerConnected || !printerAcceptsCommands) {

resources/qml/SaveButton.qml

@@ -12,6 +12,8 @@ Rectangle {
     id: base;
     UM.I18nCatalog { id: catalog; name:"cura"}
 
+    color: "transparent"
+
     property real progress: UM.Backend.progress;
     property int backendState: UM.Backend.state;
     property bool activity: Printer.getPlatformActivity;
@@ -80,6 +82,7 @@ Rectangle {
         anchors.top: progressBar.bottom
         anchors.topMargin: UM.Theme.getSize("default_margin").height
         anchors.left: parent.left
+        color: "transparent"
 
         Row {
             id: additionalComponentsRow

resources/qml/SidebarHeader.qml

@@ -207,6 +207,7 @@ Column
 
             width: parent.width * 0.55 + UM.Theme.getSize("default_margin").width
             height: UM.Theme.getSize("setting_control").height
+            color: "transparent"
 
             ToolButton {
                 id: variantSelection

resources/qml/SidebarSimple.qml

@@ -32,6 +32,7 @@ Item
         anchors.left: parent.left
         width: base.width * .45 - UM.Theme.getSize("default_margin").width
         height: childrenRect.height
+        color: "transparent"
 
         Label
         {
@@ -224,6 +225,7 @@ Item
         anchors.left: parent.left
         anchors.right: parent.right
         height: childrenRect.height
+        color: "transparent"
 
         Label
         {
@@ -469,6 +471,7 @@ Item
         anchors.left: parent.left
         width: parent.width
         height: childrenRect.height
+        color: "transparent"
 
         Label
         {