1. In a small bowl, sprinkle gelatin over 1/2 cup of the blood orange juice. Let stand until softened, about 5 minutes.
2. In a large bowl, whisk yogurt until smooth; set aside. Bring milk, heavy cream and 1/3 cup of the sugar to a low simmer. Turn off heat. Stir in vanilla and juice-gelatin mixture; mix until gelatin is dissolved. Pour into bowl with yogurt and whisk until smooth.
3. Coat eight 6-ounce ramekins with nonstick cooking spray. Pour mixture evenly among ramekins. Cover with plastic wrap and refrigerate for at least 6 hours or up to 2 days.
4. In a small pot or pan, bring remaining 1/3 cup sugar, remaining 1/4 cup blood orange juice and the orange zest to a simmer. Cook until sugar is dissolved and mixture has a syrupy consistency, about 4 minutes. Cool and refrigerate in a covered container until using.
5. To serve, carefully run a paring knife around edge of each ramekin. Turn upside down onto a plate (shake if it doesn't immediately fall out). Place an orange segment on top, drizzle with blood orange syrup and, if desired, garnish with mint.