In medium bowl, mix 2 3/4 cups flour, the baking powder and salt. In large bowl, beat shortening with electric mixer on medium speed 30 seconds. Gradually add 1 1/2 cups sugar, about 1/3 cup at a time, beating well after each addition and scraping bowl occasionally. Beat 2 minutes longer. Beat in egg whites, one at a time, beating well after each addition. Beat in vanilla and food color. On low speed, alternately add flour mixture, about one-third at a time, and strawberry mixture, about half at a time, beating just until blended. Stir in rhubarb.