Enzymes are sometimes called biological catalysts
That's called Parasthesia.
Mutations are disruptions in the human body
We need to know the dominant and recessive traits of the noombats in order to answer this question. If both of them has yellow as the dominant trait, then green may be recessive. In that case there is a chance for them to have a green bellied child. Its impossible to tell the percentage though because we don't know enough about the animals.