I remember the days PMUA where the color code was as follows
United First ( international) = GOLD
United Business = Silver
United Economy = Blue
Boarding passes and ticket jackets were that color. Ticket jackets were distrusted on international flights only and disappeared around 2003
Later United Economy Plus got gold boarding passes
This later went to all the same color
CO always had blue and gold boarding passes on super thin paper stock. So thin it was pointless.
Ticket jackets disappeared in 2005-2006.