Stools are brown due to the breakdown products of bile being that colour. The exact shade of brown of stools is influenced strongly by diet and pale brown stools are normal. Bile is produced in the liver. Very pale or clay coloured stools can be indicative of a problem with the production of bile but can also be caused by changes in diet. Tan colour sounds okay for a stool but if you are worried and the colour stays the same on non fast days get it checked by your doctor. To put your mind at rest if nothing else.