diff --git a/gtk2_ardour/automation_line.cc b/gtk2_ardour/automation_line.cc
index acc6cffd0e..98b87ee6e6 100644
--- a/gtk2_ardour/automation_line.cc
+++ b/gtk2_ardour/automation_line.cc
@@ -244,7 +244,10 @@ AutomationLine::set_line_color (uint32_t color)
 {
 	_line_color = color;
 	line->set_outline_color (color);
-	line->set_fill_color ((color & 0xffff00) + 80); // XXX TODO configurable transparency
+
+	ArdourCanvas::SVAModifier mod = UIConfiguration::instance().modifier ("automation line fill");
+
+	line->set_fill_color ((color & 0xffffff00) + mod.a()*255);
 }
 
 void
diff --git a/gtk2_ardour/themes/dark-ardour.colors b/gtk2_ardour/themes/dark-ardour.colors
index 42b4e57456..caf27d02a9 100644
--- a/gtk2_ardour/themes/dark-ardour.colors
+++ b/gtk2_ardour/themes/dark-ardour.colors
@@ -503,6 +503,7 @@
   <Modifiers>
     <Modifier name="audio bus base" modifier="= alpha:0.3"/>
     <Modifier name="audio track base" modifier="= alpha:0.3"/>
+    <Modifier name="automation line fill" modifier="= alpha:0.3"/>
     <Modifier name="automation track fill" modifier="= alpha:0.3"/>
     <Modifier name="covered region base" modifier="= alpha:0.7"/>
     <Modifier name="crossfade alpha" modifier="= alpha:0.1803"/>