I've had a problem a few times now where Neck Diagrams will crash and close while using the Color Palette to change the "Outline Colour" on Fretboard Settings.

I attempt to "Drag and Drop" the color of choice into "Dropper" from the RGB Slider and the program immediately crashes.

If need be I can provide the crash report from my latest attempt.

Neck Diagrams 2.2.1 running on Mac OS Big Sur.