There is no rhyme or reason for Ford's use of colors on connectors. However, the color codes on wires seems to have some consistency. For example, the black-blue stripe wire used for door activated courtesy lights on 64-66 Mustangs is the same color wire on my 1999 E-250 Van. It's identified as wire "53" for both, and I assume for years in between. There are other wire colors that Ford used over the years, the green-yellow stripe wire, code "54", used for hot all the time lights, glove box for example, or a hot lead to the clock, for another example. It was strange when I was wiring my Van to see familiar colors for the same functions. It's probably Ford's desire to NOT reinvent the wheel for each model year.
Jim