Is there a color palettes folder/file?
The color palettes, which are delivered with LibreOffice, are stored in /installation-folder/share/palette. Those with filename extension .soc are for colors. Colors, which you have defined yourself are stored as single items in the file registrymodifications.xcu in your LibreOffice user profile folder. Customize color palette files work too, if they are stored in the folder config in your LibreOffice user profile folder.
Color palette files are easily editable with an editor, but there exists currently no tool, to extract the items from the file registrymodifications.xcu to a color palette file. You need to do it manually, if you will exchange the colors between different PCs for example.