Why pool tables are green
Pool (called "billiards" by those who think it sounds more classy) is actually a distant cousin to another sport which you may not guess at: Croquet. Croquet, that good old game played out on the lawn with mallets and big stonelike orbs being shpot through hoops, has long been a popular sport. Pool is the answer to the question "How can we still play this game during the winter?"
Someone (no one really knows who) decided to try to make an indoor version of the game that is suitable for all seasons, times of day, and temperatures. He got to work building the first ever pool table (who knows - maybe even using that fancy croquet mallets in the process), which was a simple enough concept to start. Some of the ideas didn't work so well indoors. We had to be sure that the balls didn't go flying off the table so we added bumpers. To make the new game's rules go smoother it changed from hoops to holes (or "pockets"). Also, as a final touch, to make those pool balls sail smooth as glass over the surface, we put some felt on top of the pool table.
So, why green? Well, that only makes sense. At first, people were trying to "pretend" they were playing croquet, so the green color is supposed to serve as a "fake lawn." So, the next time that someone comes to you with the line "Why are billiard tables green?," just smirk and say - "We can thank croquet."