LiteIcon looks great, but it cannot change the system icons since El Capitan/10.11 - something to do with System Integrity Protection
[http://freemacsoft.net/liteicon/sip.html]
The workaround (disable protection, reboot, run app, enable protection, reboot) seemed a bit risky to me (security-wise), so I:
- Booted my Mac from an old 10.7.5 external recovery disk
- Found the relevant files, and replaced them manually.
Here is the script that I used to do this manipulation. It depended on a few sets of icons I had already downloaded.
SYSTEM=/Volumes/MacOSX/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources
cd $SYSTEM
mkdir BAD
mv ApplicationsFolderIcon.icns BAD
mv BurnableFolderIcon.icns BAD
mv DesktopFolderIcon.icns BAD
mv DeveloperFolderIcon.icns BAD
mv DocumentsFolderIcon.icns BAD
mv DownloadsFolder.icns BAD
mv GenericFolderIcon.icns BAD
mv GroupFolder.icns BAD
mv LibraryFolderIcon.icns BAD
mv MovieFolderIcon.icns BAD
mv MusicFolderIcon.icns BAD
mv OpenFolderIcon.icns BAD
mv PicturesFolderIcon.icns BAD
mv PublicFolderIcon.icns BAD
mv ServerApplicationsFolderIcon.icns BAD
mv SitesFolderIcon.icns BAD
mv SmartFolderIcon.icns BAD
mv SystemFolderIcon.icns BAD
mv UsersFolderIcon.icns BAD
mv UtilitiesFolder.icns BAD
#
# Downloaded some icons from:
# http://yosemiteicons.deviantart.com/gallery/52150606/Folder-Sets
#
# Sadly, some of them don't have replacements:
#
cd /Volumes/MacOSX/Users/nigel/Downloads
cp -pr "./Flader Transparency Original/Applications/Applications.icns" $SYSTEM/ApplicationsFolderIcon.icns
cp -pr $SYSTEM/BAD/BurnableFolderIcon.icns $SYSTEM
cp -pr "./Flader Transparency Original/Desktop/Desktop.icns" $SYSTEM/DesktopFolderIcon.icns
cp -pr $SYSTEM/BAD/DeveloperFolderIcon.icns $SYSTEM
cp -pr "./Flader Transparency Original/Documents/Documents.icns" $SYSTEM/DocumentsFolderIcon.icns
cp -pr "./Flader Transparency Original/Downloads/Downloads.icns" $SYSTEM/DownloadsFolder.icns
cp -pr "./Flader original/Generic/Generic.icns" $SYSTEM/GenericFolderIcon.icns
cp -pr $SYSTEM/BAD/GroupFolder.icns $SYSTEM
cp -pr "./Flader default part2/icns/Library.icns" $SYSTEM/LibraryFolderIcon.icns
cp -pr $SYSTEM/BAD/MovieFolderIcon.icns $SYSTEM
cp -pr "./Flader Transparency Original/Music/Music.icns" $SYSTEM/MusicFolderIcon.icns
cp -pr $SYSTEM/BAD/OpenFolderIcon.icns $SYSTEM
cp -pr "./Flader Transparency Original/Pictures/Pictures.icns" $SYSTEM/PicturesFolderIcon.icns
cp -pr "./Flader Transparency Original/Public/Public.icns" $SYSTEM/PublicFolderIcon.icns
cp -pr $SYSTEM/BAD/ServerApplicationsFolderIcon.icns $SYSTEM
cp -pr $SYSTEM/BAD/SitesFolderIcon.icns $SYSTEM
cp -pr $SYSTEM/BAD/SmartFolderIcon.icns $SYSTEM
cp -pr "./Flader default part2/icns/System.icns" $SYSTEM/SystemFolderIcon.icns
cp -pr "./Flader default part2/icns/User.icns" $SYSTEM/UsersFolderIcon.icns
cp -pr "./Flader default part2/icns/Utilities.icns" $SYSTEM/UtilitiesFolder.icns
A few commands might also be necessary, to refresh the icons, after booting back off your 10.11 or 10.12 disk
sudo find /private/var/folders/ -name com.apple.iconservices -exec rm -rf {} ;
sudo rm -rf /Library/Caches/com.apple.iconservices.store
killall Dock
killall Finder