Add option to override the UI color

* Add -color option to core plugin which will override
   the base UI color for that session.

Reviewed-by: thorbjorn

src/plugins/coreplugin/coreplugin.h

@@ -54,6 +54,8 @@ public slots:
     void remoteArgument(const QString&);
 
 private:
+    void parseArguments(const QStringList & arguments);
+
     MainWindow *m_mainWindow;
     EditMode *m_editMode;
 };