Here's a pic of the driveshaft and some of the rear axle and brake components
The pink stripe shows up on all of the K-code mustangs of this time period that I looked at (that I could get a read on driveshaft stripes anyways - many were painted black.). That said, there were many different stripes on cars I saw that had been restored. One had 2 purple stripes adjacent to the pink, some had a single white, sometimes the white and the pink placement was reversed. I have no idea what the placement or color of the stripes indicates, only that he pink seems to be common to the K-codes of this period regardless of the rear axle ratio, tire size (15" or 14"), or whether they had inside or outside snap rings on the U-joints. The original K cars if this period, all had the pink stripe roughly 10" from the u-joint weld. The stripe 6" further towards center from the pink was orange on this car and one other had a stripe in this location. This car has a 3.89 rear axle, inside snap rings, the other had a 4.11, outside snap rings, so this has apparently nothing to do with axle ratio or snap ring type unless my interpretation of the color on the 4.11 car was wrong - stripe could have been white or yellow but too hard to tell for sure because the driveshaft was painted black. White or orange may designate the snap ring type, but more data is needed to determine for sure. I will note, that all of the driveshafts with a white stripe had outside snap rings, but again, more data is needed to be conclusive. One other thing, the trans yoke on K-codes is beefier on the ends than the D codes of this period, and has sloppily applied green paint on it.