OctaneC4D Use RGB Color Picker.
Is not interactive(Not Friendly)
Octane Standalone have live(realtime?) picker.
Want Use Enhanced Color Table or Octane Standalone Style Color Picker.
i can swith to standart color pickers, but this will not allows immediately updates while dragging the sliders. Also a note, you should change input color profile to linear to matching colors with octane's color space.