It looks like this Part has been superseded by LEGO Part 61252 Plate Special 1 x 1 with Clip Horizontal [Thick Open O Clip].
Click on a colored part below to see the Sets and MOCs that use part 6019 Plate Special 1 x 1 with Clip Horizontal [Thick U Clip] in that color. You can find an overview of all LEGO Colors here.
If a color is missing, it probably needs to be added to a Set Inventory.
This part has been used by MOCs in the following colors but not officially released.