I once went to a supply house (I think in San Diego) picking up materials for a 100A to 200A service upgrade. I asked for 40' of 3/0 THHN and I went to the back with the counter guy to grab the 2" rigid I also ordered when I glanced at some large purple wire in what looked like a cut pile. I asked about it, and he said that stack had been there for years, and he had no idea who ordered it in the first place. The wire turned out to be 4/0 THHN (General Cornish brand) 50' or so..and he gave it to me ½ price..
The H.O. thought it was beautiful
Other than that, black w/ a couple wraps of phase tape.. I have come across red #2 before, and someone taped it for their neutral...
