This is an "at one's own risk" manual, in agreement with Matt!
1. create a new empty AT5-palette in the palette editor (also as additional palette possible).
2. select any color (in the example red = 12).
3. save the palette.
4. export the palette (as *.rmpxml - file).
5. open the palette in editor "Notepad". The new monochrome palette is ever the last.
6. copy a few lines " <int>12</int> ", so that increase the number of " <int>12</int> " lines (in the sample 20)
7. save again as *.rmpxml - file.
8. open the palette editor. Delete all previous own palettes (otherwise al redoubles) and import the *.rmpxml - file.
9. now select the different colors.
10. result (the palette in pic. Is even longer than 20 colors). Note: The colors in this pic. only applicable with HDS units!!!
Best wishes
fjordfisher
Result with one other 24 color palette and a bit transparency: