Unicorn

Unicorn was a very old colour you could of painted your Neopet with, unfortunately this colour never made it that far and was retired and was replaced with the Unicorn Gem. And all of the pets that were painted unicorn were changed to the colour Red. And then ultimately, the Unicorn Gem was renamed to the Uni Gem. This colour might of been a precursor to the Uni, probably leading to the deletion of the unicorn colour, so there would later on be no confusions, which that line has been crossed a few times with confusions of which colour is what and what neopet is what, so they really had no need to delete the colour Unicorn.