Here is a blank palette grid for creating your own custom palettes.
1. Goto File > Import Image File, then select the template
2. using the Fill tool fill as many of the grid as you like
3. Give the Palette a name and genre (i.e. fantasy, baroque, etc.) if you like.
4. When Palette is complete export it: File > Export Image File...
5. Now Select the image as your color picker as follows: Tools > Color Options > Select Custom Picker From Disk...