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

config/packages/pcm_icon.yaml

@@ -2,18 +2,16 @@ when@dev:
     pcm_icon:
         directories:
             - '%kernel.project_dir%/public/icons'
-        palletes: []
+        colours: []
 
 when@prod:
     pcm_icon:
         directories:
             - '%kernel.project_dir%/public/icons'
-        palletes: []
+        colours: []
 
 when@test:
     pcm_icon:
         directories:
             - '%kernel.project_dir%/tests/icons'
-        palletes:
-            - []
-
+        colours: []