Fix device state text color in devices

Fixes #414

src/core/utilities.cpp

@@ -56,6 +56,7 @@
 #include <QPoint>
 #include <QRect>
 #include <QSize>
+#include <QColor>
 #include <QMetaEnum>
 #include <QXmlStreamReader>
 #include <QSettings>
@@ -984,6 +985,10 @@ QString ReplaceVariable(const QString &variable, const Song &song, const QString
   return variable;
 }
 
+bool IsColorDark(const QColor &color) {
+  return ((30 * color.red() + 59 * color.green() + 11 * color.blue()) / 100) <= 130;
+}
+
 }  // namespace Utilities
 
 ScopedWCharArray::ScopedWCharArray(const QString &str)