1971 280SL, 1988 300CE TT, 1994 E320 CAB, 1999 AMG C43, 2005 AMG G55K 2008 CLK63 AMG BLACK SERIES
I Googled "Mercedes Panther Black' and saw an ad for a 2005 CLS supposedly "Panther Black".
Panther Black is not a Merc paint colour name and in 2005 the only black colours Merc had was the basic 040 Black and Obsidian Black.
Panther Black is a Ford colour. I suspect someone who's familiar with it has just decided that any metallic black car is Panther Black. Years ago you used to see all sorts of cars advertised as being Masons Black (a Rolls-Royce colour), although I doubt that any of them had actually been repainted in the correct RR shade.