Grab a pint glass and add 3-5 drops of green food coloring. Make sure to add the coloring first and the beer after! Stick with classic liquid green food coloring that comes in the little squeeze bottles. (Adding blue to yellow-hued beer seems like a clever alternative, but you’ll end up with turquoise beer.)
Use a light-colored beer such as a pilsner or pale ale. The lighter the beer, the brighter the color. Slowly pour beer into the pint glass and watch the color mix as the beer goes in. If you want the coloring more vibrant add a drop or two more of food coloring.