QmlDesigner Icon for Gradient List button

Change-Id: I875f15e06b39362247f9ee3c020acf125358c506
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

share/qtcreator/qmldesigner/propertyEditorQmlSources/imports/HelperWidgets/ColorEditor.qml

@@ -518,8 +518,8 @@ Column {
                 height: 20
                 visible: colorEditor.supportGradient
 
-                color: "white"
+                color: Theme.qmlDesignerButtonColor()
-                border.color: "white"
+                border.color: Theme.qmlDesignerBorderColor()
                 border.width: 1
 
                 ToolTipArea {
@@ -566,15 +566,14 @@ Column {
                     }
                 }
 
-                Rectangle {
+                Image {
-                    width: 18
+                    id: image
-                    height: 18
+                    width: 16
+                    height: 16
+                    smooth: false
                     anchors.centerIn: parent
-                    color: "steelblue"
+                    source: "images/icon-gradient-list.png"
-
+                }
-                    border.color: "black"
-                    border.width: 1
-
                 MouseArea {
                     anchors.fill: parent
                     onClicked: {
@@ -582,7 +581,6 @@ Column {
                     }
                 }
             }
-            }
 
             ExpandingSpacer {
             }