Black gums are due to melanin pigmentation. Which is removed by depigmentation procedure. And yellowness may be due to flourosis or in general. Due to water. Or any other reason. Kindly visit a dentist nearby.
Hi. It must be calculus about whom you are talking. Plaque is a transparent invisible layer which gets removed by brushing only. You have to maintain your oral hygiene after a dentist does Scaling, it's entirely in your own hands after that.