I just purchased a P224/P229C 357Sig barrel in recent factory packaging advertised as "broached" marked: BARREL, 224, 357, DLC. It was medium gray in color, shiney, & appeared to be uncoated. After cleaning it with Slip 2000 EWL it turned dark gray. Inside the tip of the barrel & inside the first 1/8 inch of the chamber were rainbow's. Was this a barrel ready for Nitride but never made it?

I was always under the impression that a broach is just a cutting tool used to cut steel (in most cases I know of, and to the purposes of which we're talking, to cut the rifling of a bore, though it could be used externally, too). I didn't think it would affect how they 'coat' their barrels. I do, however, have P228/P229 barrels that are either phosphate or nitride; the phosphate giving it the appearance you're describing, though I don't think Sig does that for recent production barrels. I guess I'm at a loss.

It is neither phosphate or nitride, appears to be uncoated

Very odd. I'd think they'd have to treat it in some way or coat it with something. You wouldn't happen to have pics?

DLC stands for diamond like carbon. Sounds like the color may just be "off" compare to normal Sig coloring. http://www.jabuie.com/ionbond.html