To make the sour mix, combine sugar and zest in a medium bowl, using your fingers to rub the zest evenly into the sugar. Pour sugar into a small saucepan along with 1/2 cup water. Bring mixture just to a simmer, stirring to dissolve the sugar. Take the mixture off the heat, and let cool completely. Stir in the blood orange and lemon juice, then strain into a clean jar. Store in the fridge until ready to use (for up to 1 week). You’ll have enough sour mix for 7 to 8 drinks.