Note there are many favoriting icons spread in the images and images/icons. Some are for categories, others are for users and tags, others are for all of them but when used in question lists, etc.
Assuming you are looking at exactly the same favoriting entity in the same location in 2 different browsers and you see it differently after changing the file, then it is very likely that you just need to clear your browsers cache. Or you could as well open a private window, login, and see if the icon is updated.