For the tooling plate I would make that from 4140 or 4340, or at least one of the 4xxx series of steel. Good strength and reasonably easy to machine. Can be heat treated if desired.
For the tool holder, I would use 4150, or maybe a heavy truck axle or hydraulic cylinder rod if you can find one at a scrap yard. Since you are local, Clackamas Steel has a bunch of hydraulic cylinder rods on the shelf at reasonable prices, to the left of the drive through. But before I went through the work of building one from scratch, I would see if it's possible to modify an existing holder.
In this case, the blackening is most likely an artifact from the heat treatment, prior to finish grinding. There are several methods of blackening steel if you want to do that, I personally use gun bluing for my projects.