Preheat oven to 180 degrees, and place 2 6-cavity silicone dome molds on a baking tray bottom side up. Lightly spray domes with nonstick spray.
In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites to soft peaks on medium speed, then slowly add in granulated sugar. Turn speed to high, and beat whites until stiff and glossy. Whisk in food coloring to reach a lemon yellow shade. Sift in the powdered sugar and fold to fully incorporate. Working in batches, transfer mixture to a pastry bag fitted with a 5 to 9 mm tip.
Starting at the bottom of the domes, pipe meringue in a consecutive spiral from the bottom to the top of the domes, taking care to have no holes in the shape. Make a peak at the top of the dome for the ends of the lemons. Place in the bottom rack of the oven to bake for 45 minutes. The meringue should not change color, but should be crispy on the outside and still slightly marshmallow-like on the inside. Let meringue cool 10 minutes in the oven, then remove and gently remove from mold.