Plastic Pipe Question / Problem?

[DD716TED]

I live in a newer manufactured Home (1999) that was built with type of plastic pipe (color tan not grey white or black). During the current counter top replacement project in the kitchen, I noticed that the pipe area just under the hot / cold water shut off valves (kitchen sink) was discolored from the yellow color of the pipe to a deep rust/orange color??? I have inspected all areas around and under this area and there seems to be NO sign of water, water damage, or leakage in the past or present. None of the fittings are rusted or even corroded. Everything is bone dry. I have attached a picture of the area I am talking about in hope that someone can lend an idea as to what if any, is causing this problem. What should I do?

[HayZee518]

if it's not leaking - there is no problem.

[596]

Looks like FlowGuard Gold CPVC. Not real neat, but if it aint broke.......