In a mixing bowl, beat egg whites until foamy. Sprinkle with cream of tartar and salt; beat until soft peaks form. Gradually add sugar and vanilla, beating until stiff peaks form, about 5-8 minutes. If desired, divide batter in half and fold in red and green food coloring.

Drop by rounded tablespoonfuls 1-1/2-in. apart onto lightly greased baking sheets. Press a chocolate kiss into the center of each cookie and cover it with meringue using a knife. Bake at 275 degrees F for 30-35 minutes or until firm to the touch. Immediately remove to a wire rack to cool. Store in an airtight container.