The cloth of a billiard table is green because it envolved from a lawn game

Billiard cloth (sometimes erroneously called felt) is a specific type of cloth that covers the top of the table's "playing area". Both the rails and slate beds are covered with 21-24 ounce billiard cloth (although some less expensive 19oz cloths are available) which is most often green in color (representing the grass of the original lawn games that billiards evolved from), and consists of either a woven wool or wool/nylon blend called baize.

http://en.wikipedia.org/wiki/Billiard_table

by @lentebriesje