Place the loose Tiesta tea in an infuser, and put it in a heatproof Pyrex measuring cup. Pour the boiling water over the tea and allow it to steep for 3 minutes. Remove the tea from the water. Place the brewed tea in the refrigerator until chilled.
Have two champagne flutes ready to go. Divide the chilled Fruity Pebbles tea between the two flutes. Top each with the champagne and drop two blackberries into each flute. Serve immediately.