diff --git a/core/dplugins/editor/colors/adjustcurves/adjustcurvestool.cpp b/core/dplugins/editor/colors/adjustcurves/adjustcurvestool.cpp
--- a/core/dplugins/editor/colors/adjustcurves/adjustcurvestool.cpp
+++ b/core/dplugins/editor/colors/adjustcurves/adjustcurvestool.cpp
@@ -98,7 +98,7 @@
 
     d->gboxSettings = new EditorToolSettings(0);
     d->gboxSettings->setTools(EditorToolSettings::Histogram);
-    d->gboxSettings->setHistogramType(Digikam::LRGBA);
+    d->gboxSettings->setHistogramType(Digikam::LRGBAC);
     d->gboxSettings->setButtons(EditorToolSettings::Default|
                                 EditorToolSettings::Load|
                                 EditorToolSettings::SaveAs|
diff --git a/core/libs/dimg/filters/curves/curveswidget.cpp b/core/libs/dimg/filters/curves/curveswidget.cpp
--- a/core/libs/dimg/filters/curves/curveswidget.cpp
+++ b/core/libs/dimg/filters/curves/curveswidget.cpp
@@ -647,6 +647,9 @@
 
 void CurvesWidget::mousePressEvent(QMouseEvent* e)
 {
+    if(d->channelType == ColorChannels)
+        return;
+
     if (d->readOnlyMode || !d->imageHistogram)
     {
         return;
@@ -727,6 +730,9 @@
 
 void CurvesWidget::mouseReleaseEvent(QMouseEvent* e)
 {
+    if(d->channelType == ColorChannels)
+        return;
+
     if (d->readOnlyMode || !d->imageHistogram)
     {
         return;
@@ -745,6 +751,9 @@
 
 void CurvesWidget::mouseMoveEvent(QMouseEvent* e)
 {
+    if(d->channelType == ColorChannels)
+        return;
+        
     if (d->readOnlyMode || !d->imageHistogram)
     {
         return;
diff --git a/core/libs/dimg/filters/curves/imagecurves.cpp b/core/libs/dimg/filters/curves/imagecurves.cpp
--- a/core/libs/dimg/filters/curves/imagecurves.cpp
+++ b/core/libs/dimg/filters/curves/imagecurves.cpp
@@ -330,7 +330,7 @@
 {
     int j;
 
-    if (!d->curves)
+    if (!d->curves || channel == 5)
     {
         return;
     }
@@ -365,7 +365,7 @@
     int num_pts;
     int p1, p2, p3, p4;
 
-    if (!d->curves)
+    if (!d->curves || channel == 5)
     {
         return;
     }
@@ -1155,6 +1155,7 @@
 {
     if (d->curves              &&
         channel >= 0           &&
+        channel != 5           &&
         channel < NUM_CHANNELS &&
         type >= CURVE_SMOOTH   &&
         type <= CURVE_FREE)