[macfluke]

I replaced 2 6g leads for my ac(240v) that had smaller leads... the old copper leads, one looked shiny copper and the other was a dull copper with some blackish spotting on it...

what would cause the copper to dis-color?

also I clamped an amp meter on to each lead and they both pulled 19 amps each...(dont know if that helps any)

 

[Just Bill]

Dull black copper sounds like it was overheated at some time. This can be due to a poor connection or excessive current draw. Is the insulation OK or does it also appear brittle or burned. 19A does not sound like you have an existing problem, assuming all is working OK..

 

[macfluke]

connections were tight... insulation good, no cracks, not brittle, no burning, only dull copper with some blackish spotting ...
everything was/is working normal, I was working in the panel and saw the dis-colored copper on the lead...

 

[theatretch85]

Working on my new house, I noticed the coax cable coming up out of the ground the center conductor is like black (instead of a shiny copper color). It could be the wire just being exposed to moisture that is causing the discoloration.

Since you replaced the leads with new wire, try cutting the old wire back a few inches and see if it looks the same or if its just at the very ends of the wire where it was exposed.