Not a fan of Pie menus in Blender, but Blender is very keyboard-centric. Pie menus might be more reasonable in a tablet-centric app like Krita. Still, each item in the menu needs to be super easy to see and few items, or it will become hunt-and-peck every time a menu is open. For that reason, I say no to text-only pie menus and yes to pie menus with images. Whether or not some particular thing should become a pie menu always depends on context, so case-by-case for that.
Yep, that’s why in my suggestion for colors I mentioned using a perception-adjusted color space. Then colors can even be generated programatically without worrying about contrast. Whether or not we ‘really need to color code stuff’ is debatable; I bring up the point mainly for the tools, which can be colored in sections (i.e. the selection tools can all be blue-tinted). That I would find useful.