According to my "go to" authority on bugling, the earliest notation of the modern call of To the Color is found in the 1874 U.S. Army Infantry manual (Upton Manual). "To the Colour" is the bugle call for the companies to march to the parade ground to form as a full regiment. In other words, "march to the flag or color." See the Taps Bugler site for a full history of the call: https://www.tapsbugler.com/to-the-color/