Which flags should I enter to c4d.gui.ColorDialog?
It worked when I entered 0 as a default flag but I want to learn more about other options.
ColorDialog is just the Python version of C++'s GeChooseColor() function.
It uses the flags DR_COLORFIELD_ICC_BASEDOC and DR_COLORFIELD_ICC_BPTEX which just define the proper color profile. Typically is is enough to just set 0.