In contrast with the other colours like purple, you could dye blue easily. The most important dye-stuffs were Indigo which came from India and an a local material called "Färberwaid". For the production of this special leaves mixed with human urine were fermented in buckets. To intensify the process alcohol had to be added. As alcohol was very expensive at that time, the dyers drank it and so the alcohol then was enriched in the urine.
The clothes had to be kept in the bucks for about 12 hours which was mostly done on Sundays. Then they were hung up on a string to the get the blue colour developed. On Monday, when the dyers lay drunken beside the clothes and waited for the result, everybody knew that the dying process was carried out, die dyers were "blue". Therefore in the German language the word "blue" means also "drunken". Also the "blue Monday" has his origin from this process (Thomas Seilnacht)