Green plumbing is not a good sign. Though, it is not entirely unexpected either. Copper is more vulnerable to corrosion than other metals.
As you may have guessed, the green coloration is the color of copper when it is corroding. This is normally something that you find on older piping. It is also a sign that it may be time to get new piping. In this video, you will learn more.
Copper corrosion is often caused by your water chemistry. An abundance of minerals in your water can lead to corroding of the piping. Further, the water from your water heater may also be corroding your piping. This happens when the sacrificial anode rod in the water heater is not replaced frequently enough. The result is metal flakes that get into the piping and settle on the copper. This is why you may see corrosion in splotches. Plumbers often recommend replacing the metal anode every three to five years to prevent this from happening. It is almost always cheaper to prevent a problem then to clean up from a problem. You will be thanking yourself later.