This is a remix of a David Warboss Wet palette. It works basically the very same. I just changed the size of the magnets and also the size of the entire palette.
This size is 154x154mm to have a bit bigger area where you can place your colours.
Once the prints stops insert the magnets with a small drop of glue on them to keep them in place while printing the next layers.
Or you can use a negative volume to remove the top layers on top of the magnet holes and glue the magnets after the print is finished.
The 3mf files includes all the settings above and were exported from Prusa Slic3r so in case you will use it there the print stop and layer height should be setup, just double check the settings.
Hope that original author don't mind that I will borrow Prusa's video on how to use it.
And as always I am adding also the source file to Fusion360 that you can adapt the print to your needs in case you need to make any changes. The project does include list of parameters so it should be easy for you to make small modifications in case you have different magnets or you want different size of your palette.
The author remixed this model.