--- a/Image.st	Wed Oct 05 17:33:49 2016 +0200
+++ b/Image.st	Fri Oct 07 10:14:54 2016 +0200
@@ -13751,6 +13751,10 @@
 
 !
 
+nColorsUsed
+    ^ self realUsedValues size
+!
+
 pixelArraySpecies
     "return the kind of pixel-value container in rowAt:/rowAt:put: methods"