To make the sugar syrup, add the xylitol (or white sugar) and ⅓ cup water to a wide saucepan over low heat. Bring to a boil, constantly stirring, until sugar has dissolved. Then turn off the heat and allow it to cool for around 7-10 minutes.
Once it has cooled down, you can use it in the drink.
To prepare the drink, boil the water in a large saucepan, then turn off the heat. Add the tea leaves, stirring them around and pressing them against the sides of the pot for a few minutes, to get the color out.
Let the tea sit for 10 minutes in the hot water. Then strain the tea through a sieve into a pitcher, to remove the extra leaves.
Add the sugar syrup and an optional amount of lemon juice at this time, giving it a good stir. If you don't add in any lemon juice, the color will stay blue. By adding in more lemon, juice, it will start to turn purple! See the "Color Change" section below.