Hi,
According to some gun historians, William Bailes was the first maker to intentionally color caseharden and preserve the colors as decoration. That was around 1760. I don't believe it became really popular in England until the last decade of the 18th century and I doubt many American gun makers were doing it until well into the 19th century. I don't believe it would be appropriate for a Lehigh pistol but then again, English and European styles found traction in the big cities such as Philly so by the early 19th century, who knows.
dave