What Causes Dark Coloured Breast Discharge?

In a 54 yr old female, could darker than normal breast discharge (tea vs. light yellow) only noted with expression be a pre menopausal issue? Mamo was clear and so was Ultra sound. Started in right breast 2 yrs ago and three months later is in the left. Only one duct exit is dark thick sticky fluid on each breeast and the rest are the clear to light yellow sticky that s been present since having children at age 32 and 35.What are the next steps if any? GP is suggesting surgeon?