The Zbrush icon is nice but I always find it difficult to locate in the dock, it sort of just disappears so I’ve made a couple of replacement icons, one just has a bit of an orange blur behind it, and the other has a blurry black edge. To replace the icon use the get info command. I’m on a Mac, I don’t know if Windows PC’s can use an icns file.
The zip folder also contains the original icon so you can restore it. http://www.filedropper.com/icnsfiles