Preheat oven to 175 degrees. Combine egg whites, sugar, and meringue powder in heatproof mixer bowl, and set over simmering water. Whisk until sugar dissolves and whites are hot, 2 to 3 minutes.
Transfer bowl to mixer. Use whisk attachment to whisk on low speed, increasing to high, until stiff, glossy peaks form, about 10 minutes; add vanilla.
Tint meringue by stirring in food color. Transfer to a pastry bag with a petal tip (we used Ateco No. 102 and No. 104 to create two sizes). Using a small dot of meringue, attach a 1 1/2-inch square of waxed paper to a flower nail. Twirl nail clockwise as you hold the bag at a 45-degree angle and press out icing. Slide waxed paper off nail and place on baking sheet. Continue, placing only same-size roses on each tray. Bake trays of roses 30 to 60 minutes or until dried through (times will vary with size of meringue). Let cool completely, and store in airtight containers.
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