If you are on Windows insider program, a new Build 21343 just got rolled out. One noticeable changes are the new Windows Explorer icons and numerous other bug fixes as well.
If you are not too found of those changes, you can actually revery back the icon. Thankfully there is a little piece of software by door2windows called CustomizerGod.
CustomizerGod allows you to change icons instantly without going to system wide level to apply those icons and you can revert them back easily or change to another pack and gives you a wide range of options from change taskbar icons to file explorer icons.
First you will need to have admin rights to run the app. Then go to general icons and select all of them. After that, select export resources and that will back up all of your current icons into a folder. If Windows ever gets updated to the new icon pack, you can always load up the exported resources and apply the old icons back.