Heat oven to 350 degrees. Line 24 regular-size muffin cups with paper liners.
CUPCAKES: In large bowl, beat cake mix, gelatin, water, 1/3 cup Key lime juice, vegetable oil, and egg whites, with an electric mixer on low speed for 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Using a toothpick, add green gel food coloring, if desired. Using an ice cream scoop, divide batter evenly among muffin cups, filling each about two-thirds full.
Bake 18 to 20 minutes or until toothpick inserted in center comes out clean. Cool in pan for 10 minutes. Remove from pan to a cooling rack. With toothpick, pierce the tops of the cupcakes in several places.
GLAZE: In small bowl, whisk together 1 cup confectioners' sugar and 2 to 2 1/2 tablespoons Key lime juice until glaze is smooth and thin enough to drizzle. Drizzle and spread glaze over cupcakes. Cool completely, about 30 minutes.
FROSTING: In large bowl, beat cream cheese and butter on medium speed until light and fluffy. Add 1 tablespoon Key lime juice, and 2 1/2 cups confectioners' sugar, beat on low speed until combined. Using a tooth pick, add green gel food coloring until you reach desired color. Continue to beat on medium speed until light and fluffy. Frost or pipe cupcakes. Decorate with blue, green, and white, sprinkles or lime peel. Store covered in the refrigerator.
Cook's Note: You can use fresh or bottled Key lime juice. If Key lime juice is not available, use regular fresh or bottled lime juice. Try our Seahawk Blue Raspberry Cupcakes too!