Hello! There are different ways you can desaturate an image, Luminosity is a really useful one.
When you want to work with color neutralization, it’s important to keep similar values, colors naturally have different values (a blue red color with value 100 will be darker than a yellow with the same value.)
Luminosity desaturation takes into account those differences, which makes it really useful to work with color neutralization, abstraction, etc…
That’s why I think a view mode that temporarily shows your canvas desaturated with the Luminosity method would be really useful. Other software like Gimp and Krita already have it.
Here’s more info:
https://docs.gimp.org/2.6/en/gimp-tool-desaturate.html
http://pixeljoint.com/forum/forum_posts.asp?TID=10695