From around the 1630s a brown wash was regularly applied to strengthen the rims, thin out the fragile glaze and maybe sometimes to imitate a silver or copper band. Historically it is a defining feature of the Shunzhi period (1644-61) porcelain and can in rare occasions be found on Song to Yuan dynasty bowls Qingbai bowls.
The glaze used for this was the most simple possible and the same as used for the "batavia" browns discussed in another thread. The base was "yellow earth" according to information given in the first of Pere the Entrecolle's letters from Jingdezhen in 1712, or in other words, mud. Depending on iron content or other impurities - your guess - the colors turned out different over the years and actually within the batches of similar porcelain. Still we can find an average preference depending on maybe fashion, causing a larger percentage of the porcelains turning out in different shades.
During the Kangxi period a light beige color was most common, during the early Qianlong period a full chocolate ("High Batavia") brown was most common and for a short period in-between, around Yongzheng a dark coffee brown was the preferred shade. See for examples the cups and saucers with this brown coming out from the Ca Mau find.
A direct comparison can be made with the shade of the surface covering so called Batavia wares.