I happen to see on this page: http://www.ivillagehealth.com/experts/digestive/qas/0,,242109_170252-2,00.html
the comment 'The third major type of gallstone is the brown pigment stone, formed by calcium and bilirubin because of infection of the bile.' I've done the flush twice, the larger, older stones appear brown, newer ones tan or green; perhaps related to recurrent urinary infections I've had.