The further oxidation of tea polyphenols deepened the color. A cup of clear green tea, especially at high temperature for a long time, will lose its green color and increase its yellow color. This is the yellow-red and reddish-brown oxidation products formed by the oxidation of tea polyphenols in tea, mainly theaflavins, thearubigins, theabrownins and so on. These products are non-toxic and will not cause harm to human body.