Thank you for the review. :D
"D" calls the quick color pie. It brings up hardcolded colors. This menu can be used with directional selection. Directional selection is when you hold "D" and just quickly swipe the mouse in the direction of the pie item you want to select. This is very fast.
The "Z" hotkey brings up the "Precise Colors Pie". The colors in this menu are not hardcoded. You can customize the colors in this menu but directional selection does not work. The Colors of the "Precise Color Pie" can also be set in the side bar (often known as N-Panel) of the Node editor.
You can customize your shortcut keys in the Addons preferences.
As soon as the Blender Python API gives me a way to have customizable colors and directional selection I will merge the two menus into a single one. But at the moment it is not possible to have these two features in one pie menu.
But why are there two shortcut keys and can’t select one of them?