When can you visibly see the darkening around the nipples and the appearance of the milk glands during pregnancy?

This usually happens around the last month of pregnancy. Sometimes it doesn't happen (leaking) until right up to the delivery date. But around the last 3-4 weeks is usually around the time you will start leaking and so forth. Actually I started seeing the veins and darkening of nipples around four months and started leaking colostrum "pre-milk" at 5 1/2 months so everyone is different hope this helps, Good Luck and God Bless!!!