Dave,
As far as I know Track does not cast any replacement parts for our locks. When we get cast parts back from the foundry they are always a light gray color due to the sand blasting cleanup process they use. Parts that are to be hardened and tempered after casting are first packed in a carbon rich material, heated to 1600 degrees for 4 to 5 hours, and slowly cooled. This does two things: it restores the carbon lost in the surface of the part during casting, and it softens the part so that it can be drilled or (in the case of springs) have the tension set. This heating process always gives the part a dark color. So, the frizzen you received is simply a raw casting that has been annealed.
In the case of frizzens, we heat them to around 1550 using an oxyacetylene torch burning a carbonizing flame and quench in a light oil. If our frizzens are quenched in water they will usually break at some point. We draw them back at around 390 to 400 for one hour.
Hope this helps.