If 'Interpolation' selected as 'UNI-Palette' - then image colors will be interpolated to colors of UNIVERSAL palette (UNI). In that palette all colors have own cells: blue and red and green and yellow and gray and all another. But their total count - is 256. It is small number. Because of it PaintCAD is cheating and interpolate all colors (16 millions) in these 256 UNI-colors. You can force PaintCAD to interpolate colors by searching nearest colors in UNI-palette. Is it 'JoyRight'-'Adaptation'-'Simple'.