Here are three more tips if you want to make green beer for St. Patrick's Day......
1. It works best with light beer, like a lager or pilsner. The lighter the beer, the greener it'll look. So things like Bud Light and Coors Light work well.
2. Use somewhere between 2 and 5 drops of green food coloring per beer. It depends on what type of beer you use, and what shade of green you want. So try it with two drops first, then add more if it's not green enough. Here's the Betty Crocker way
3. Add the food coloring to your glass BEFORE you pour the beer in. It mixes better that way, so don't need to use a spoon or slosh it around. (If you want to mix MASS quantities, here's how to do it with kegged beer.)