“Felt effect “ on cookies.

I used colored icing sugar (aka confectioner’s or powdered sugar) for the felt effect. But right before coating the dried royal icing surface with the sugar, I used a paint brush to apply random dabs of flooding-consistency royal icing.
My tutorial:
https://cookieconnection.juliausher.com/blog/made-by-manu-a-warm-hug-for-a-cookie-mug