Which coloring agents are responsible for the color in red tea and yellow tea?
I believe that it is the different polyphenols (Flavonoids are a type of polyphenol) in tea that give it its colors. Black tea has thearubigins that give it a red-brown color. The yellow color in tea comes from theaflavins. The color of the tea also depends on the acidity of the water used, because thearubigins are very weak acids, and the anions they produce have strong colors. If the water you use is alkaline, the color will be stronger. If it is acidic, the color will be lighter.