How to set HTML-files icon to default?
You could also try to run

rm -r /var/folders/*/*/*/com.apple.iconservices
rm -r /var/folders/*/*/*/com.apple.dock.iconcache
rm -r ~/Library/Caches/com.apple.finder
qlmanage -r
sudo rm -r /Library/Caches/com.apple.iconservices.store


and restart.