Take for example the setting menu from stock Android: Yes, there are still icon but they all have the same color and it is really difficult to tell them apart. Every time I go to settings I have to search around until I find the settings I was looking for. If it had colorful icons then navigation would be easier because my brain would learn "blue icon = keyboard settings"
Or take Chrome on Android: Open Chrome, press the three dots on the bottom right for the menu and try to find the 'search in page' entry. Every time i wanna search something I have to read half of the menu items to find the search function... If it would have a distinct icon it would be much easier to find.