Word formation

Hallo! I have a doubt about word formation: is colouring only a noun or also an adjective? I’ve found in the monolingual dictionary that it is only a noun but my classmates have found out online that it isn’t true… Thank you very much! Agnese.

Usually colouring is a noun, but it can also be a verb (he is colouring the book). The only adjective we can think of is “colouring pens” i.e. pens used for colouring.