Darkening copper water supply lines

Just inspected a house in which the copper water supply lines have turned black in the small utility room. The pipes at the fixtures are fine. There is a battery backup for the sump pump in this utility room. Wondering if this is the cause of the darkening due to sulfur gas being produced by the battery. Didn’t notice strong sulfur odor however. Can’t determine any other reason. Also, does this darkening of the copper accelerate deterioration/corrosion of the pipes and do I need to bring it up as a defect.

Did you check the humidity in the space. Seems like you have a combination of both high humidity and possibly high levels of dissimilar metals in the water…both in the lines and in the moisture in the air. Just a thought…

The copper piped that has turned black, maybe substandard pipe with impurities. I know in the 70’s imported piped from China and Korea was cheap and had a lot of impurities. Perhaps this is imported pipe?

Is there any drywall in the vicinity? Is it possible that Chinese drywall is to blame?

Chlorine stored there or a cat litter box can cause grief too.