diff --git a/assets/text/TODO b/assets/text/TODO
index b8d85f3..ce7ba75 100644
--- a/assets/text/TODO
+++ b/assets/text/TODO
@@ -11,7 +11,7 @@
 High-priority list:
 1)  unit tools: arrow, {cloud,speech bubble}, curve, measure, pick, polygon, triangle, unicode
 2)  text tool: a) honour RTL text flow b) navigating w/ cursor keys c) pasting text
-3)  operators: erase, invert, rotate, scale, shift, slice, tile
+3)  operators: erase, rotate, scale, shift, slice, tile
 4)  GUI:
     a) switch to GTK
     b) replace logo w/ canvas panel in About dialogue
diff --git a/liboperators/OperatorInvert.py b/liboperators/OperatorInvert.py
new file mode 100644
index 0000000..009e7d1
--- /dev/null
+++ b/liboperators/OperatorInvert.py
@@ -0,0 +1,24 @@
+#!/usr/bin/env python3
+#
+# OperatorInvert.py
+# Copyright (c) 2018, 2019 Lucio Andrés Illanes Albornoz <lucio@lucioillanes.de>
+#
+
+from Operator import Operator
+
+class OperatorInvert(Operator):
+    name = "Invert colours"
+
+    #
+    # apply(self, region)
+    def apply(self, region):
+        for numRow in range(len(region)):
+            for numCol in range(len(region[numRow])):
+                region[numRow][numCol][0:2] = [(~r & (16 - 1) if r > 0 else r) for r in region[numRow][numCol][0:2]]
+        return region
+
+    # __init__(self, *args): initialisation method
+    def __init__(self, *args):
+        pass
+
+# vim:expandtab foldmethod=marker sw=4 ts=4 tw=120
diff --git a/libroar/RoarCanvasCommandsOperators.py b/libroar/RoarCanvasCommandsOperators.py
index 9618279..55124a7 100644
--- a/libroar/RoarCanvasCommandsOperators.py
+++ b/libroar/RoarCanvasCommandsOperators.py
@@ -6,6 +6,7 @@
 
 from OperatorFlipHorizontal import OperatorFlipHorizontal
 from OperatorFlipVertical import OperatorFlipVertical
+from OperatorInvert import OperatorInvert
 from GuiFrame import GuiCommandListDecorator
 from ToolObject import ToolObject
 import copy, wx
@@ -14,9 +15,10 @@ class RoarCanvasCommandsOperators():
     # {{{ canvasOperator(self, f, idx)
     @GuiCommandListDecorator(0, "Flip", "&Flip", None, None, None)
     @GuiCommandListDecorator(1, "Flip horizontally", "Flip &horizontally", None, None, None)
+    @GuiCommandListDecorator(2, "Invert", "&Invert", None, None, None)
     def canvasOperator(self, f, idx):
         def canvasOperator_(event):
-            applyOperator = [OperatorFlipVertical, OperatorFlipHorizontal][idx]()
+            applyOperator = [OperatorFlipVertical, OperatorFlipHorizontal, OperatorInvert][idx]()
             if  (self.currentTool.__class__ == ToolObject)  \
             and (self.currentTool.toolState >= self.currentTool.TS_SELECT):
                 region = self.currentTool.getRegion(self.parentCanvas.canvas)
@@ -56,7 +58,7 @@ class RoarCanvasCommandsOperators():
     def __init__(self):
         self.menus = (
             ("&Operators",
-                self.canvasOperator(self.canvasOperator, 0), self.canvasOperator(self.canvasOperator, 1),
+                self.canvasOperator(self.canvasOperator, 0), self.canvasOperator(self.canvasOperator, 1), self.canvasOperator(self.canvasOperator, 2),
             ),
         )
         self.toolBars = ()