What is the purpose of golf ball markers?

Answer 1

They mark their ball out of courtesy for other players as if one player on the green hits the ball of another they receive a two shot penalty. It is also so the player can clean his ball and line it up.

Answer 2

A gold ball marker has the purpose of marking where the ball was on a putting green when the ball has to be picked up. It is usually the size of a coin and is placed behind the Golf ball before the ball is picked up. The ball in then placed in front of the marker on the original spot.

Answer 3

Because the black ones won't work.