Add colour label to extension type - not working

I created a rule, very simple to make sure I knew how Hazel worked. Either I don't of Hazel doesn't for me...
I created a rule:
Name: Red Label
If ALL of the following conditions are met for THE FILE OR FOLDER BEING MATCHED
EXTENSION is .mkv
Do the following to the matched file or folder:
SET COLOR LABEL to RED
I made this rule for my desktop folder and nothing happens, no error message and it doesn't label my .mkv file red. What's wrong?
I created a rule:
Name: Red Label
If ALL of the following conditions are met for THE FILE OR FOLDER BEING MATCHED
EXTENSION is .mkv
Do the following to the matched file or folder:
SET COLOR LABEL to RED
I made this rule for my desktop folder and nothing happens, no error message and it doesn't label my .mkv file red. What's wrong?
