Icons that never change their look whatever icon theme you choose are : HARDCODED icons.
These applications have a absolute path to a picture on your system. This path will never change UNLESS YOU do something about it.
On the github you will see I use two scripts in regard with these badly performing icons.
You can run either the hardcodefixer-vx.sh and hope for the best. But not all icons will be fixed.
Then you follow the movie and see how you can do this yourself manually.
Here is an example of a little script (yellow font) that will change all the icons automatically. It is included in the install-third-party-software-vx.sh.
Only necessary if you ever want to use the application CLIPIT.