Welk

The adjective used to describe the change in colour/tone/gloss of a velvety surface when an object is scraped across it.

Toddler: "Daddy what's this I draw on the couch?"
Dad: "I don't know, son. I don't think there's a word for that."
Toddler: "It's called a welk."
Dad: "OK dude, I'll put that in Urban Dictionary."
Toddler: "It's a fire engine."