Based on the documentation, you can set a background color on an SVG icon by appending a class name of the icon container element using the following pattern:
.slds-icon-[sprite name]-[icon name]
Which is great and according to the example it works:
When I try to do the same thing for the custom sprite and one of the 100 custom icons:
It does not work.
Is the documentation wrong or am I missing something trivial here?