This is a tricky one @DannyPancratz - I tried a few things before the weekend but couldn’t get it working.  I’ve asked our more technical folks.  :)

Hey @DannyPancratz - it looks like this works:

  .icon--star:before   {
    color:transparent!important;
  }

  .icon--star:before   {
    background-repeat: no-repeat;
    background-position:top;
    background-image: url('newimagelink.png');
  }

@Kenneth R thanks, but that didn’t quite work for me. It changed the star of the Favorite/Subscribe icon, not the bookmark icon for sticky. 

I assume a similar CSS approach will probably work if I can identify the correct target for the bookmark icon. 

Also, I just reported what I think is a bug: the Sticky label seems to no longer be showing when you click into a sticky topic. 

Ah sorry @DannyPancratz - I misunderstood and thought you meant the subscribe icon.  The bookmark icon is an SVG that’s defined by .topic-view_sticky-flag.  For this one it should also be possible to override it with an SVG from another library or update the fill colour via CSS.