Replace 'palletes' with 'colours' which is a bit more intuitive and is also spelt correctly.

src/DependencyInjection/PcmIconExtension.php

@@ -26,6 +26,6 @@ class PcmIconExtension extends Extension
         $definition = $container->getDefinition('pcm_icon.icon_extension');
 
         $definition->addArgument($config['directories']);
-        $definition->addArgument($config['palletes']);
+        $definition->addArgument($config['colours']);
     }
 }