Use the same text colour for comboboxes as buttons

Given comboboxes use the same background as buttons they should use the
same text colour too.

This prevents a situation in Breeze where a ComboBox could get white
text on a white background when using a colourscope with complementary
colours.

Change-Id: I21502186178a32ce480cd3e838335451bf644c3e

src/declarativeimports/plasmastyle/ComboBoxStyle.qml

@@ -31,6 +31,7 @@ QtQuickControlStyle.ComboBoxStyle {
     label: PlasmaComponents.Label {
         text: control.currentText
         elide: Text.ElideRight
+        color: theme.buttonTextColor
         verticalAlignment: Text.AlignTop
     }
 

tests/components/combobox.qml

@@ -0,0 +1,41 @@
+import QtQuick 2.0
+
+import org.kde.plasma.components 2.0
+import org.kde.plasma.core 2.0 as PlasmaCore
+
+Rectangle {
+    id: root
+    color: "white"
+    width: 800
+    height: 300
+
+    ListModel {
+        id: demoModel
+        ListElement { text: "Banana"; color: "Yellow" }
+        ListElement { text: "Apple"; color: "Green" }
+        ListElement { text: "Coconut"; color: "Brown" }
+    }
+
+    Flow {
+        anchors.fill: parent
+        anchors.margins: 20
+        spacing: 20
+
+        ComboBox {
+            model:demoModel
+        }
+        ComboBox {
+            editable: true
+            model: demoModel
+        }
+        PlasmaCore.ColorScope {
+            implicitWidth: childrenRect.width
+            implicitHeight: childrenRect.width
+
+            colorGroup: PlasmaCore.Theme.ComplementaryColorGroup
+            ComboBox {
+                model:demoModel
+            }
+        }
+    }
+}