I have had two keys that look identical for forever, and I finally decided to do something about it. I used my two favorite spring nail polish colors, coral and mint, to color code my keys.
1.) Materials: you will need a key, nail polish, and painters tape.
2.) Cover the bottom half of your key with painters tape.
3.) Paint the top of your key with around 5 coats of nail polish. Keep painting until it becomes the consistancey you're happy with.
4.) Let dry for an hour.
5.) Unwrap the painters tape from the keys, and you're done.