It looks like a dark gray to me. But I agree with you, that the difference in color between black and that “dark gray” is too little to be noticed as “disabled”.
So I guess yes - if you want to go with the system’s behavior and Toolbar, then one should also have icons in some sort of what the system expects (or is designed for). And for an own custom design, an own custom Toolbar might be more appropriate…
Anyway - one last piece of information about the ‘native’ Toolbar (I know it has nothing to do with Windows and the OP): I don’t like that some Linux distributions place the captions alongside the Icon (rather than below, such as macOS and Windows) by default. With more than just a couple of Buttons, there isn’t enough space to fit them all.
If that’s an issue for you, too - then I can post a Declare we’re using to change the Toolbar-Style on Linux.