Steep the tea in a glass with 1/2 cup boiling water. Cool to room temperature. Once cooled, pour tea into a bowl. Sprinkle gelatin on top. Set aside.
In the meantime, place the sugar, 1/2 cup of water, and honey in a saucepan with over medium heat; cook and stir until sugar dissolves. Bring mixture to a simmer and cook without stirring until candy thermometer read 240 degrees F, about 12-15 minutes.
Pour syrup mixture into bowl over the gelatin mixture. Beat on low until combined. Increase speed to high and beat until thick and fluffy and mixture triples in volume, about 10 minutes.
Add 3 tbsp blueberry powder into marshmallow mixture and fold until combined.
Scrape mixture into prepared pan. Set aside in a cool place to set for at least 3 hours, preferably for 8 hours for a more firm marshmallow for easy cutting.
Whisk together powdered sugar, cornstarch and remaining blueberry powder until well combined.Remove marshmallow from pan and peel away parchment paper. Lightly dust top and bottom of marshmallow with powdered sugar mixture. Lightly cover a serrated knife with non-stick spray and slice marshmallows into 1” cubes.