Wow! Thank you for the images.
The fellow who kindly sold me the helmet said that it was from Surabaya (interestingly enough he said he got it from a random gardener who didn't know what it was). Very interesting about the blue paint, I guess it is almost certain it was used by the Indonesians after the war.
I guess an interior ministry or civilian helmet somehow ended up in Indonesia... very strange. I guess it would be hard to determine without wartime photos or some sort of documentation.