People who fuss about such things call the stones that are red chiang-yu-tung and stones that are grayish brown niu-chiao-tung, but there really isn't any fixed standard for distinguishing the varieties.
有好事者將印石色澤較紅者稱為醬油凍，略帶灰黃色的則稱牛角凍，其實並無確切的標準足供判別。