DrJim posted this response on our message forum:

Thoughts about the color of milk-

Fluid discharge from the breast can be clear watery, milky white, green/brown/dark or red.
When inducing there is going to be a period of time, perhaps a week or more, when the breasts feel swelled and heavy like they are full of something but nothing comes out. At this point the alveoli are turning on. They start producing some of the components of milk. These components draw water into the alveoli across the cell membranes which brings in the fluid component of the milk. When this is occurring, if you are pumping, you will begin to express a clear watery substance. Milk is not far behind. When you have just delivered a baby and your milk comes in this clear watery substance that precedes the milk is your colostrum. Red is always a sign of concern. It usually means blood. This can be due to breast trauma, even from a rough pump perhaps, but cancer in the breast is always a concern and warrants an exam by your physician. Brown and green and most of the other colors is due to what happens when the breasts stop lactating. This can occur over years even. When lactating the ducts are turgid and open. Milk flows through them etc. When breasts go through the reverse process called involution, the alveoli shut down, stop working. Many of them turn to fat. The ducts collapse, in some segments fluid behind these ducts cannot pass and collect in little pockets. The cells lining the duct system die and shed into this fluid. It is these dead cells and debris that colors this fluid green and brown. The breasts can feel lumpy and cystic due to these little trapped pockets of fluid. This is called fibrocystic breast disease with breast exams and mammograms.

So if you are inducing and get some green-brown fluid it is related to some fibrocystic process in the breasts. Here is the good news; Inducing lactation is a very good way to reverse fibrocystic breast condition. Many women with inducing can get rid of the lumpiness of the cysts in their breasts after some time. The ducts always collapse eventually after lactation stops. Even after a delivery, when their milk comes in many women experience some "plugged ducts" that have milk backed up behind them and they must massage gently to get the ducts open. This experience often occurs during induction as well, requiring massage to correct because when inducing the ducts undergo a process of reopening up.

Generally brown green is not a problem but just indicates the breasts have been "out of use" for some time and a great thing to do to correct the situation is to induce lactation.
 

Here are a couple of additional thoughts on the subject;

Cysts are always dilated segments of the ducts that alternate with the collapsed segments. The green fluid is in these cysts. When lactating the ducts are turgid, open, round and springy. When not lactating they get flacid and collapse. When inducing the Prolactin causes the cells in the ducts to start swelling and get turgid again so that they reopen. Typically when inducing nothing will come out for days and weeks, then when a collapsed segment reopens the cyst drains and suddenly you get the green fluid. The dilated segment then can heal and return to a normal function.

The process of stopping lactation or involution varies a lot among women. Some women have a difficult time lactating even after giving birth, produce small amounts of milk and quickly dry up. These are the types that are more likely to have problems with fibrocystic conditions. Other women seem to be high prolactin producers. After delivery their milk comes in with a bang and they produce lots of milk and have no problems breastfeeding for as long as they want. When they try to dry up their breasts don't seem to want to stop and it may take them quite a while. These women will often leak a little bit of creamy discharge in their bras for sometimes years. In my opinion these are the healthiest ones. Their ducts are staying open even when not lactating and all the equipment remains in good functional condition for years. If they try to induce lactation they often succeed in a very short time. Statistically women who lactate have lower rates of fibrocystic breast disease and cancer of the breast. This shows that, if anything, Prolactin does not encourage cancer, but probably is somewhat protective. Just some interesting thoughts in the support of lactation.

DrJim