Preheat oven to 325 degrees F (165 degrees C). Prepare three 9-inch cake pans by lightly greasing them, dusting with flour, and shaking out the excess.
Sift together the flour with 2/3 cups of sugar, the baking powder, and salt into a large bowl. In a separate bowl, beat together the oil, water, nectar, yolks, vanilla, and lemon zest until well combined. Pour the yolks into the flour, and mix until the batter is smooth, mix in food coloring until desired shade is reached. Beat together egg whites with the cream of tartar in a clean bowl until soft peaks form. Gradually add the 1/2 cup of sugar, and beat until stiff. Gently fold whites into batter. Pour into prepared cake pans.
Bake in preheated oven until a toothpick inserted into the center comes out clean, about 25 minutes. Run a metal spatula or small knife around the edges of the cake to loosen, and allow to cool in the pans for 10 minutes before inverting onto a cooling rack.
