In a medium bowl, mix flour, baking powder, and salt.
In another bowl, beat butter and sugar until fluffy. Add egg and vanilla; mix until smooth.
Combine dry and wet ingredients in two additions until just mixed.
Divide dough into three portions; color one red, one green, and leave one plain.
Roll each between parchment into 10-inch squares. Stack, roll into a log, and chill for 1 hour.
Slice into ¼-inch rounds and bake at 350°F (175°C) for 12–15 minutes. Cool on rack.
