Blue tea, or butterfly pea flower tea, is a caffeine-free herbal
concoction, made by seeping dried or fresh leaves of the Clitoria
ternatea plant. The best thing about the blue tea is that it is
absolutely caffeine-free, and it is packed with antioxidants. Adding
lemon juice to the tea changes the pH of the drink, making it
change colour from deep blue to purple. The tea leaves are also
used to change colour in cocktails as well.