These are colours derived from renewable sources like plants, minerals etc. Plant sources being bark, berries/fruits, leaves, flowers, roots etc
This 1000s of year old tradition was displaced by the invention of the chemical dyeing. The synthetic dyes set off the decline of the natural dyeing and also resulted in major "pollution, to the extent that the dyeing towns have become un liveable" "The water..." contamination is so high in the Tamil Nadu dyeing town of Tiruppur, where a river (noyyal) has turned totally black because of the dyeing effluents.The ground water also is highly contaminated in these areas. Taking stock of the various pollutants, long term environmental impact and our own health the world
(especially the west) is turning back to natural dyes. while each of the color derived means a host of experiments and hand process, see here for a list of colors derived fro various plants products.To help your own health and that of the environment and to revive the dy(e)ing art, support Natural dyeing. The water used is very high. If virtual water is taken in to account it is way higher. But be assured the natural Korra colour of cotton without any additional process and colour is any day the best- environmentally!