Wanted to do a mix of color study methods, namely painting in color, while seeing in Greyscale.
I did this by a variety of methods, including making a color sphere of warms and cools (didn't matter the color), and using a Custom Proof setup to display the canvas in Greyscale. That way, I could select "values" instead of "colors" and do a standard portrait study.
Thanks to Marco Bucci, Anthony Jones, and Ahmed Aldoori for the tips, tricks, and methods! I think this is a super-cool, organic way to get some colors on your canvas you may not expect!