The following directions should return the default Utilities folder icon. Open the Terminal.app and copy and paste the following commands one at a time into the Terminal.app, press the return key after each copy and paste.
defaults write com.apple.finder AppleShowAllFiles -bool true
killall Finder
This will reveal all the hidden files on OS X in the Finder application. Navigate to the /Applications/Utilities folder in the Finder. You should see a file named Icon. If the file exists then move it to the Trash and empty the Trash. Now return the Finder to its normal state.
defaults write com.apple.finder AppleShowAllFiles -bool false
killall Finder
Log out then log back in.