Prepare Lemon or Lime Gelatin using only ½ cup sugar. For orange gelatin, dissolve the gelatin and sugar in 1 ⅓ cups boiling strained orange juice instead of water (add the lemon or lime juice as directed). For grapefruit gelatin, omit the lemon or lime juice and dissolve the gelatin and sugar in 1 ⅔ cups boiling strained grapefruit juice instead of water. If using zest, substitute 1 teaspoon orange or grapefruit zest.