One question, is the tubing type M(red writing on it), L(blue writing.
or K (Green writing) I would not worry about K(heaviest) or L. M is
the lightest, but would not be a problem for a scratch. If it is a
gouge, you may get a seepage leak years from now, but probably not. I
can't imagine that it would burst in any case.

Cold lines usually tarnish, probably due to oxidation due to high
relative humidity in their environment when the pipe is cold. Room
temperature pipe or warmer would not cause this.

Stretch