Place egg whites in a large bowl; let stand at room temperature for 30 minutes. Sift flour and 3/4 cup sugar together twice; set aside. , Add the cream of tartar, salt and almond and vanilla extracts to egg whites; beat on medium speed until soft peaks form. Gradually add remaining sugar, about 2 tablespoons at a time, beating on high until stiff glossy peaks form and sugar is dissolved. Gradually fold in flour mixture, about 1/2 cup at a time., Gently spoon half of batter into an ungreased 10-in. tube pan. To the remaining batter, stir in the orange zest, orange extract and, if desired, food colorings. Gently spoon orange batter over white batter. Cut through both layers with a knife to swirl the orange and remove air pockets., Bake on the lowest oven rack at 375° for 30-35 minutes or until lightly browned and entire top appears dry. Immediately invert pan; cool completely, about 1 hour., Run a knife around side and center tube of pan. Remove cake to a serving plate.