mjseakan, Hemikiller's response is closer to what actually happened. 6B (Light Yellow Gold) is a RPO (regular production option) that was offered from the start of 73 production until it was replaced in 1/73 by 6C Medium Yellow Gold. Although it was also offered on Maverick, Pinto and Thunderbird, it does not show on most printed matter that you can find now.
As Jason stated, if it had been a DSO special order there would have been four digits after the 12, which is the ordering district, Buffalo. The section on your door label where the paint code is listed would also be blank.
Adding to the confusion is that most of these colors went by two names. There is the Vehicle Division promotional name which named the color when originally designed. Then when the paint is released for service, the Ford Parts Division gets to put their own name on the paint. So 6B Light Yellow Gold becomes Light Goldenrod and 6C Medium Yellow Gold becomes Medium Goldenrod. And of course Lincoln/Mercury Division got to use the fancy names so as not to be confused with the commoners who drive Fords !