Try killall -KILL Finder in Terminal. Usually clears up graphical glitches.

If that doesn't work, follow these steps to reset the Icon Services cache:

sudo find /private/var/folders/ \
-name com.apple.dock.iconcache -exec rm {} \;

sudo find /private/var/folders/ \
-name com.apple.iconservices -exec rm -rf {} \;

sudo rm -rf /Library/Caches/com.apple.iconservices.store

After the first command, it will prompt you for a password. Enter your login password. After all three commands are run, reboot the Mac.

Try killall -KILL Finder in Terminal. Usually clears up graphical glitches.

Try resetting Finder preferences. Run these commands in Terminal:

rm ~/Library/Preferences/com.apple.finder.plist
killall -KILL Finder

Note that you will have to redo any Finder preferences you had set.

If that doesn't work, follow these steps to reset the Icon Services cache:

sudo find /private/var/folders/ \
-name com.apple.dock.iconcache -exec rm {} \;

sudo find /private/var/folders/ \
-name com.apple.iconservices -exec rm -rf {} \;

sudo rm -rf /Library/Caches/com.apple.iconservices.store

killall -KILL Dock
killall -KILL Finder

After the first command, it will prompt you for a password. Enter your login password.