diff --git a/cura/ExtruderManager.py b/cura/ExtruderManager.py
index f5971ac141..edd6ab7d23 100644
--- a/cura/ExtruderManager.py
+++ b/cura/ExtruderManager.py
@@ -191,9 +191,10 @@ class ExtruderManager(QObject):
         container_registry.addContainer(container_stack)
 
     ##  Generates extruders for a specific machine.
+    #
+    #   \param machine_id The machine to get the extruders of.
     def getMachineExtruders(self, machine_id):
-        container_registry = UM.Settings.ContainerRegistry.getInstance()
-        if not machine_id in self._extruder_trains:
+        if machine_id not in self._extruder_trains:
             UM.Logger.log("w", "Tried to get the extruder trains for machine %s, which doesn't exist.", machine_id)
             return
         for name in self._extruder_trains[machine_id]:
diff --git a/cura/ExtrudersModel.py b/cura/ExtrudersModel.py
index 3265667dc6..960c05bd5e 100644
--- a/cura/ExtrudersModel.py
+++ b/cura/ExtrudersModel.py
@@ -28,6 +28,10 @@ class ExtrudersModel(UM.Qt.ListModel.ListModel):
     #   containers.
     IndexRole = Qt.UserRole + 4
 
+    ##  Colour to display if there is no material or the material has no known
+    #   colour.
+    defaultColour = "#FFFF00"
+
     ##  Initialises the extruders model, defining the roles and listening for
     #   changes in the data.
     #
@@ -71,7 +75,7 @@ class ExtrudersModel(UM.Qt.ListModel.ListModel):
 
         if self._add_global:
             material = global_container_stack.findContainer({ "type": "material" })
-            colour = material.getMetaDataEntry("color_code", default = "#FFFF00") if material else "#FFFF00"
+            colour = material.getMetaDataEntry("color_code", default = self.defaultColour) if material else self.defaultColour
             item = {
                 "id": global_container_stack.getId(),
                 "name": "Global",
@@ -80,9 +84,9 @@ class ExtrudersModel(UM.Qt.ListModel.ListModel):
             }
             self.appendItem(item)
 
-        for extruder in manager.getMachineExtruders(global_container_stack.getBottom()):
+        for extruder in manager.getMachineExtruders(global_container_stack.getBottom().getId()):
             material = extruder.findContainer({ "type": "material" })
-            colour = material.getMetaDataEntry("color_code", default = "#FFFF00") if material else "#FFFF00"
+            colour = material.getMetaDataEntry("color_code", default = self.defaultColour) if material else self.defaultColour
             position = extruder.getBottom().getMetaDataEntry("position", default = "0") #Position in the definition.
             try:
                 position = int(position)
diff --git a/cura/SettingOverrideDecorator.py b/cura/SettingOverrideDecorator.py
index 06dbc2cb31..23730fee60 100644
--- a/cura/SettingOverrideDecorator.py
+++ b/cura/SettingOverrideDecorator.py
@@ -1,11 +1,10 @@
 # Copyright (c) 2016 Ultimaker B.V.
 # Cura is released under the terms of the AGPLv3 or higher.
 
-from PyQt5.QtCore import pyqtSignal
 import copy
 
 from UM.Scene.SceneNodeDecorator import SceneNodeDecorator
-
+from UM.Signal import Signal, signalemitter
 from UM.Settings.ContainerStack import ContainerStack
 from UM.Settings.InstanceContainer import InstanceContainer
 from UM.Settings.ContainerRegistry import ContainerRegistry
@@ -15,9 +14,10 @@ from UM.Application import Application
 ##  A decorator that adds a container stack to a Node. This stack should be queried for all settings regarding
 #   the linked node. The Stack in question will refer to the global stack (so that settings that are not defined by
 #   this stack still resolve.
+@signalemitter
 class SettingOverrideDecorator(SceneNodeDecorator):
     ##  Event indicating that the user selected a different extruder.
-    activeExtruderChanged = pyqtSignal()
+    activeExtruderChanged = Signal()
 
     def __init__(self):
         super().__init__()
diff --git a/plugins/PerObjectSettingsTool/PerObjectSettingsPanel.qml b/plugins/PerObjectSettingsTool/PerObjectSettingsPanel.qml
index 4610083674..03158266f5 100644
--- a/plugins/PerObjectSettingsTool/PerObjectSettingsPanel.qml
+++ b/plugins/PerObjectSettingsTool/PerObjectSettingsPanel.qml
@@ -36,6 +36,7 @@ Item {
                 {
                     id: extruders_model
                 }
+                visible: extruders_model.rowCount() > 1
                 textRole: "name"
                 width: items.width
                 height: UM.Theme.getSize("section").height
diff --git a/resources/definitions/fdmprinter.def.json b/resources/definitions/fdmprinter.def.json
index 52aab1d26c..1f7ed7c78a 100644
--- a/resources/definitions/fdmprinter.def.json
+++ b/resources/definitions/fdmprinter.def.json
@@ -324,7 +324,6 @@
                     "minimum_value": "0.001",
                     "minimum_value_warning": "0.04",
                     "maximum_value_warning": "0.8 * machine_nozzle_size",
-                    "default_value": true,
                     "settable_per_mesh": false,
                     "settable_per_extruder": false
                 },
@@ -338,7 +337,6 @@
                     "minimum_value": "0.001",
                     "minimum_value_warning": "0.04",
                     "maximum_value_warning": "0.8 * machine_nozzle_size",
-                    "default_value": true,
                     "settable_per_mesh": false,
                     "settable_per_extruder": false
                 },
@@ -353,6 +351,7 @@
                     "default_value": 0.4,
                     "type": "float",
                     "value": "machine_nozzle_size",
+                    "settable_per_mesh": true,
                     "children":
                     {
                         "wall_line_width":
@@ -366,7 +365,6 @@
                             "value":"line_width",
                             "default_value": 0.4,
                             "type": "float",
-                            "default_value": true,
                             "settable_per_mesh": true,
                             "children":
                             {