I wrote a program that loads Commodore-64 multicolor pixel art images in the "koala" file format, and displays them to a regular Commander X16 320x200 graphics screen.
The C64 uses a fixed palette of 16 colors for all its graphics.
I do find that the saturation of the default colors in de c64 palette in the Cx16 emulator is not very good though: when the images are displayed on a C64 or in an emulator like Vice for instance, they look much better in my opinion.
So the program sets a custom palette (the "pepto" Vic-II colors) to make the images look closer like they would on a C64.
This program has been integrated in a multi-format image viewer now, the source code of that is here https://github.com/irmen/prog8/tree/master/examples/cx16/imageviewer