A great collection of medals that were designed to work for any game genre.
They come in:
Suggestion: If your game challenges have some relationship to a UI element, you can use the medal with the closest color of that UI element.
For example, in "Complete level x without taking damage", there's an implied connection with the "health bar", and if we assume its color is green, then this will also be the color of our medal.
The more color variations you use in your achievements table, the more beaultiful they'll look to your players.