To make cupcakes, combine flour,baking powder and salt in a medium bowl.
Beat butter and sugar with an electric mixer on medium speed until light and fluffy. Add eggs; mix until smooth. Add half of flour mixture, and combine; repeat with remaining flour mixture. Add yogurt and vanilla; blend at low speed. Blend in zest. Scoop dough into 48 mini baking cups (about 2/3 full); bake until tops spring back when touched lightly in center (about 10 minutes).Remove from oven; cool completely.
To make frosting: Place cream cheese in a medium bowl; beat with an electric mixer on medium speed until smooth and creamy. Add powdered sugar,vanilla,grapefruit zest and juice;beat until smooth.
Divide the frosting into 2 bowls. Add food coloring to one bowl; mix with a spatula until frosting is light pink. Frost cupcakes.
NEAT IDEA TO FROST CUPCAKES:
PUT FROSTING IN A PIPING BAG WITH A LARGE ROUND TIP (OR USE A ZIP TOP PLASTIC BAG WITH A CORNER CUT OFF), AND PIP A LARGE DOLLOP ON TOP OF EACH CUPCAKE. THEN USE ANOTHER BAG WITH A SMALLER TIP AND A DIFFERENT COLOR FROSTING TO MAKE A "BULL'S EYE" ON TOP OF EACH DOLLOP.