Taro milk tea is typically a boba drink of purple color that is flavored with taro (whether that is powder or from real taro roots which gives it the purple color).
Taro roots contain anthocyanins, a type of pigment that gives it its purple hue.
Taro milk tea typically uses jasmine green tea, but any type of green or black tea works.
You can also use loose green tea leaves, just make sure to strain the leaves once the tea has steeped.