Why does Color Picker offer colors when I'm working in a Grayscale document?
My document mode is Grayscale, but when I use the Color Picker, it offers me colors. Specifically, When I do an Edit -> Fill and set K=20% (see below), the color actually added has unequal R, G, and B components (208,209,211). After filling, if I check the color with the eyedropper, it reads 18%, not 20%. Clearly, I misunderstand Grayscale mode. What is the correct way to fill with a specific K value?

Photoshop 21.0.3 on Windows 10.
