Pineapple Grapefruit Swirl

• In a metal ice tray stir together 1 cup of the grapefruit juice and the sugar if desired until the sugar is dissolved. 
• Fit the tray with the divider, and freeze the mixture until it is frozen solid. 
• In anther metal ice tray fitted with the divider pour 1 cup of the pineapple juice and freeze it until it is frozen solid. 
• The fruit mixtures may be prepared up to this point 1 day in advance. 
• In a blender blend the frozen grapefruit juice mixture with 1 1/2 ounces of the tequila and the remaining 1/4 cup grapefruit juice, scraping down the sides occasionally, until the mixture is smooth but still frozen and divide the mixture between 2 stemmed glasses. 
• In the cleaned blender blend the frozen pineapple juice with the remaining 1 1/2 ounces tequila and the remaining 1/4 cup pineapple juice, scraping down the sides occasionally, until the mixture is smooth but still frozen and divide the mixture between the 2 glasses.