I’ve come across a quote by Teddy Roosevelt which shows his admiration for Alexander Hamilton. It uses the phrase “the touch of the purple,” but supplies little hint as to what it means.
Roosevelt saw in Hamilton “the touch of the heroic, the touch of the
purple, the touch of the gallant.”
The best explanation I’ve found is a possible religious meaning, gleaned from the phrase’s inclusion in this Wikipedia article. I am also aware that purple has a connotation of royalty or nobility in that, some centuries ago, purple dyes were extravagant and therefore used as a symbol of wealth and power. I’m not entirely convinced that either of these are the sense that Roosevelt was invoking.
Here, purple is used as noun. So, if you check the definition of purple according to the Merriam Webster especially 2 of 3 entry and particularly 2a, you will find exquisite definition of purple:
imperial or regal rank or power
Backed by Google definition:
a crimson dye obtained from some molluscs, formerly used for fabric worn by an emperor or senior magistrate in ancient Rome or Byzantium.