Put an 8-inch square glass baking dish in the freezer to chill.
Combine the sugar with 2 cups water in a medium saucepot over medium-high heat. Bring to a simmer to dissolve the sugar, about 5 minutes. Remove the pot from heat, add the pea flower tea and steep until the simple syrup turns a deep indigo, about 15 minutes; strain. Cool to room temperature, about 5 minutes.
Whisk the coconut milk into the syrup. Pour the mixture into the chilled baking dish and freeze for 1 hour. Rake the mixture with a fork and freeze for another hour. Rake and freeze for 1 hour more. Rake one final time before serving.
Serve the granita with the lemon wedges on the side. Invite your guests to squeeze the lemon over the granita and watch the color change from a cool blue to a vibrant purple.
You can purchase pea flower tea from specialty tea stores and online retailers such as Amazon.
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