I found a 3rd issue DS for sale, with a matte finish that looks almost just like a 2nd issue Agent.  I can't find any information out there that this might have been a factory finish... is this something exceedingly rare, or just a refinish?
 

If it is marked DS it is a refinish. However there was a Commando which was a matte finish DS that was produced concurrently with the Agents that were matte finish during the strike era.

There was a black matte finish version of the Detective Special called the "Commando Special" made during the big Colt strike of the mid-80's.
This is not to be confused with the Colt Commando of WWII, which was a parkerized Official Police.

During the strike, Colt didn't have enough skilled workers to polish all the models so they made special strike versions of some guns with flat black unpolished finishes.
The strike version of the Trooper Mark V was the Peacekeeper.
The strike Detective Special was the Commando Special.

Other than that, there never was a matte blue finish actual Detective Special, all had polished bright blue finishes.

I suspect you have a refinished Detective Special.

Thanks guys... Upon a closer look of the photos, this one actually was a Commando Special.  I was aware of the Peacekeeper before, but not this model.  I wound up passing on it because I found a proper DS with gorgeous finish for the same money.

Another stupid question - what speed loaders have worked well for you with D-frames?  I've read that S&W K-frame speed loaders should work, and I can see how that's possible with HKS speed loaders that leave some wobble with the cartridges.  I'm wondering if Safariland K-frame speed loaders would work, since they have a very rigid hold on the cartridges and they don't catalog a model for the D-frame.

I like strips, but I have a couple of HKS speed loaders, and I believe that is right S&W K frame loaders work with Colt D frame. I'd have to go find them to be certain.