diff --git a/gtk2_ardour/themes/adwaita_dark-ardour.colors b/gtk2_ardour/themes/adwaita_dark-ardour.colors
index dfc7f739b0..de091f4c14 100644
--- a/gtk2_ardour/themes/adwaita_dark-ardour.colors
+++ b/gtk2_ardour/themes/adwaita_dark-ardour.colors
@@ -175,6 +175,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/blueberry_milk-ardour.colors b/gtk2_ardour/themes/blueberry_milk-ardour.colors
index 118bfc4a17..5ac0f5aa7b 100644
--- a/gtk2_ardour/themes/blueberry_milk-ardour.colors
+++ b/gtk2_ardour/themes/blueberry_milk-ardour.colors
@@ -172,6 +172,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/caineville-ardour.colors b/gtk2_ardour/themes/caineville-ardour.colors
index 42d1d369e3..3e52a1bc26 100644
--- a/gtk2_ardour/themes/caineville-ardour.colors
+++ b/gtk2_ardour/themes/caineville-ardour.colors
@@ -173,6 +173,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/captain_light-ardour.colors b/gtk2_ardour/themes/captain_light-ardour.colors
index f0f2816d6b..14c17efb4d 100644
--- a/gtk2_ardour/themes/captain_light-ardour.colors
+++ b/gtk2_ardour/themes/captain_light-ardour.colors
@@ -174,6 +174,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/clear_gray-ardour.colors b/gtk2_ardour/themes/clear_gray-ardour.colors
index b6574e7725..d88a721689 100644
--- a/gtk2_ardour/themes/clear_gray-ardour.colors
+++ b/gtk2_ardour/themes/clear_gray-ardour.colors
@@ -173,6 +173,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/cubasish-ardour.colors b/gtk2_ardour/themes/cubasish-ardour.colors
index 8728d44d2a..1e18f2c17c 100644
--- a/gtk2_ardour/themes/cubasish-ardour.colors
+++ b/gtk2_ardour/themes/cubasish-ardour.colors
@@ -173,6 +173,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/dark-ardour.colors b/gtk2_ardour/themes/dark-ardour.colors
index 9c15757d68..2a72b00774 100644
--- a/gtk2_ardour/themes/dark-ardour.colors
+++ b/gtk2_ardour/themes/dark-ardour.colors
@@ -175,6 +175,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/diehard3-ardour.colors b/gtk2_ardour/themes/diehard3-ardour.colors
index 0c7247bdb3..74df9a7cea 100644
--- a/gtk2_ardour/themes/diehard3-ardour.colors
+++ b/gtk2_ardour/themes/diehard3-ardour.colors
@@ -174,6 +174,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/recbox-ardour.colors b/gtk2_ardour/themes/recbox-ardour.colors
index 8c7f8c4b43..2c6471eece 100644
--- a/gtk2_ardour/themes/recbox-ardour.colors
+++ b/gtk2_ardour/themes/recbox-ardour.colors
@@ -174,6 +174,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>
diff --git a/gtk2_ardour/themes/unastudia-ardour.colors b/gtk2_ardour/themes/unastudia-ardour.colors
index 71d69f1c1b..6281b435a5 100644
--- a/gtk2_ardour/themes/unastudia-ardour.colors
+++ b/gtk2_ardour/themes/unastudia-ardour.colors
@@ -172,6 +172,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:yellow"/>
diff --git a/gtk2_ardour/themes/xcolors-ardour.colors b/gtk2_ardour/themes/xcolors-ardour.colors
index 0e8b2053bf..aaa84ec63a 100644
--- a/gtk2_ardour/themes/xcolors-ardour.colors
+++ b/gtk2_ardour/themes/xcolors-ardour.colors
@@ -173,6 +173,7 @@
     <ColorAlias name="gtk_processor_postfader_frame" alias="widget:green"/>
     <ColorAlias name="gtk_processor_prefader" alias="widget:ruddy"/>
     <ColorAlias name="gtk_processor_prefader_frame" alias="widget:ruddy"/>
+    <ColorAlias name="gtk_scrollbar_slider" alias="neutral:midground"/>
     <ColorAlias name="gtk_send_bg" alias="theme:bg1"/>
     <ColorAlias name="gtk_send_fg" alias="widget:blue"/>
     <ColorAlias name="gtk_solo" alias="alert:green"/>