Update background with luma and chroma ref for L C curves Color and Light

rtgui/diagonalcurveeditorsubgroup.h

@@ -95,6 +95,7 @@ public:
     void pipetteDrag(EditDataProvider *provider, int modifierKey) override;
     void showCoordinateAdjuster(CoordinateProvider *provider) override;
     void stopNumericalAdjustment() override;
+    void updateLocallabBackground(CurveEditor* ce) override;    
 
     bool curveReset (CurveEditor *ce) override;
 
@@ -102,6 +103,7 @@ protected:
     void storeCurveValues (CurveEditor* ce, const std::vector<double>& p) override;
     void storeDisplayedCurve () override;
     void restoreDisplayedHistogram () override;
+    void restoreLocallabBackground() override;
     void savePressed ();
     void loadPressed ();
     void copyPressed ();