Because the new DATlib 0.1 supports dark bit colors now, I wanted to figure out which RGB-255 color will be translated to which Neo-Geo RGB-63 color code by the "buildchar.exe".
The following color chart is the result of my research. Any color value has been double checked with the "palettes.s" file and Furrtek's NGPG palette tool (ngpg01.exe).
I have assigned all RGB-255 values to the corresponding RGB-63 colors values (except of color 1 ($0000), pure black with dark-bit off) and hope this color chart will be useful for other developers.