I had exactly the same problem as this gentleman
https://community.usa.canon.com/t5/Professional-Photo-Printers/ix-6820-printing-photos-in-purple-ins...
However reinstalling the latest drivers (dated 2017) did NOT cure the problem
The blackest areas of the image are printing in light purple.
I checked all the obvious things like reported ink levels, clean heads etc.
I then tried printing the test patern and the BK stripes were blank.
On examination the BK cartridge was empty even though the printer was not nagging about it.
Replacing the cartridge did not cure the problem imediately, but after running a couple of cleaning cycles the BK stripes finally appeared and normal service was resumed.
So, after 100s of false "cartridge empty" warning messages when they were good for another 50 pages or more, it finally got it wrong the other way round!
