Hong Kong police are spraying protesters with blue-dye water cannons to mark them for arrest later

Slick idea.

https://www.insider.com/hong-kong-police-fire-blue-dye-water-cannons-2019-8?fbclid=IwAR2hz2jZNVPXS3QkUQIsgTJn_u5KdxowXhCVtsQdOmzE7N0Ak5dT7gHp0cM