In this study, in order to investigate the natural colorants of black tea, various test methods were developed and set upped. For this purpose, methods for measuring natural tea pigments, polyphenols, synthetic dyes, some metals and the pH of the extract were developed. The results of measuring natural tea pigments showed that Iranian tea has higher natural pigments (chlorophyll, pheophytine and their derivatives) than foreign tea. The results of analysis of polyphenols showed that foreign tea compounds have higher polyphenolic compounds and therefore the colour of the extract was much richer than the colour of Iranian tea extract. Examination of synthetic colours also showed that there is no synthetic colour in any of the foreign or Iranian tea samples. Heavy metal testing with ICP-OES also showed that foreign tea has more metals, especially aluminium, than Iranian tea. Also, measuring the pH of Iranian and foreign brewed teas showed that the extract of foreign teas is more acidic than the extract of Iranian teas. According to the results, it can be concluded that the origin of the difference in the colour of brewed tea extract is primarily due to the variety of tea itself and its proper processing and fermentation process, which can lead to higher formation of theaflavins and thearubigins (natural red pigments). On the other hand, high concentrations of aluminium and polyphenolic compounds in foreign tea can also lead to the formation of coloured complexes (orange to red) and more colourful tea colour.