Greg, the iron in the mix may slightly affect the color, but more variable is the wood stained. Unless it's from the same tree, no two stocks will be the same color. Each stock will vary by the amount of sugars, and tannins in the wood. Across maples, it should be close, as it will across ash, and so on. You might try adding some more steel, to see if you still get a reaction, but it's probably used up, though still acidic as far as PH, so you should still neutralize. I like ammonia over baking soda. Last you mix should still be OK, but may need to be strained of sediment.
Bill