Most of the world celebrates it on 1st May.
According to https://www.norden.org/en/info-norden/public-holidays-greenland May 1st in both International Workers Day and Anniversary of introduction of home rule. These are not public holidays, but provide time off under collective bargaining agreements. So Greenland should be striped Red, Green, Gray and one more color.
Lol thats truly unique
The map certainly isnt perfect. Austria for example should be yellow since we official just celebrate an ominous “state holiday” and nothing else. Which essentially was just a compromise in order to not anger the bourgeoisie back when it was made a holiday.