It looks like old copper that has discolored with age. Picture is too blurry to be positive, but it's probably just surface corrosion and nothing to worry about.

A few seconds with a bit of emery cloth should tell you if that's copper under that paint/patina/whatever.

A much more urgent question in my mind is, "What are you going to do about the exposed electrical wiring (!) UNDER THE SINK, of all places????"

It's copper plumbing... and it's funky wiring.

There's no excuse for that connection not to be in the disposal and and not having a romex clamp on there. What's more... unless I'm not seeing something... the garbage disposal isn't grounded. That's something that you should take care of ASAP.