Purple interlinear had an interesting appendix on the cross, which was changed in the navy blue interlinear. I'm sure there are other changes...
I don't get it...a jw & ebay thing
The Watchtower's purple KIT (1969) page 1158, misquotes Dana and Mantey's A Manual Grammar of the Greek New Testament in an attempt to support their "a god" translation of John 1:1. However, Dr. Mantey protested the Watchtower's dishonest use of his work and threatened a lawsuit. That may have been a reason for the blue revised KIT in 1985 in which quotations from Dana and Mantey are absent.
By the way my company's second hand bookstore has a copy of the purple (1969) KIT for sale at $25.00. This was a surprise for me because in the past our bookbuyers never purchased Watchtower books. However, I purchased my copy at a Convention in 1969 for $2.00. Glad I still have it. Maybe it will be worth $50.00 in a few years.