In 8.1.6, when you use the Dark Sidebar, you cannot follow the instructions here to change MenuItem icon colors without changes to the core SCSS.
_sidebar-dark.scss would appear to control the colors, so after much digging, setting $icon-color to null on Line 39 should have done the trick... but it didn't.
After wanting to flip my desk over for about 45 minutes, I started searching for $icon-color elsewhere in the project. It turns out that setting $icon-color to null on line 33 of _header-dark.scss is what allowed the
.menu-icon-primary class to take over.
I believe this should be corrected so that the css options on Menu can be properly implemented. Right now the extra CSS in the theme seems unnecessary if you can just set color options on the menu container... and the theme clearly has no problem applying extensive class options elsewhere.
Thank you for your feedback on this. We will check it further and apply the necessary code improvements.
In your case, It turns out that setting $icon-color to null is the right since the customization by
_sidebar-dark.scss overrides the default menu state color options.
In the near future, we will be doing significant improvements based on the new Figma Design system to optimize the HTML and CSS file size.