"Cleanskin" meaning untattooed in Australian English
Solution 1:
It seems the AusEng slang meaning, untattooed, is derived from "unbranded", an animal whose skin is NOT permanently marked with a symbol by means of a branding iron
cleanskin
noun mainly Australian
1. an unbranded animal
2. slang
a person without a criminal record
3. a terrorist who has no obvious links to terrorist groups, and who thus does not appear on police watch lists
4. Australian and New Zealand
a bottle of wine whose label does not display the producer's name
Collins Dictionary