There have been very limited "Unusual or special" liveries which have slipped by over the years but most common ones are known by all - World Click, 95 years, 100 Years, The Pandas on BFT, and BioFuel but heres a list of some uncommon liveries on one-off airplanes:
This is PH-BFR
with a special slogan written in Dutch: H14 bedankt! "Het acceptatie team"
This was also the last KLM 747 to receive a D-Check in Hangar 14.
This is PH-BFL
It's currently still sitting at AMS as of August 14, 2020 retired with no certain future planned. PH-BFT, BFV, and BFW remain in cargo operation, and BFN has reportedly been sold to a scrapper, and is being prepped for a final flight to the desert to be retired, but BFL still sits at AMS. BFL is sitting engine-less (1 or 2 engines missing), and with no livery but it did receive a special name/sticker commemorating KLM 747 Fleet Manager Robert Van Bohemen. (The plane was reportedly moved last night)
This is PH-BFO
I don't recall this airplane having any unusual livery (that wasn't a popular well known livery like mentioned above) but this airplane seems to be the only one to have had an air to air session for videos or photos. This seems to be the only photo I could find online of PH-BFO. Quite a popular one.
Here's KLM being lazy or weird or something. They love to take their time to remove stickers once they have done their time. One airplane is missing the swan but has the "world click" slogan (BFU), and one is missing the "world click" slogan (BFY).
This livery was very short lived as well. It was seen on many KLM 747 before Northwest merged with Delta, and KLM Joined Skyteam. Its their straight cheatline livery with the KLM/NW Logo in a position near where the "Skyteam" logo is today. As you can see, the AirFrance-KLM logo is missing, and the placement of the city names is in the place of that logo. (When KLM did join Skyteam and the Air France Alliance - those 2 extra stickers on KLM liveries became the new standard and regular)