Buzz - the 2013 price list indicates that H&H guns come either "colour hardened or bright finish."
As I understand it, the case hardening is the last step in the process, after all the action shaping, filing, parts fitting and engraving. Once the action has been case hardened, the surface should not be altered (e.g., drilling pin holes) because that breaches the carbon "skin" left by the hardening.
Here is a pic from Turnbull's website of an Elsie he re-color case hardened. One but not all of the pin holes has a circle around it: