A <a href="https://en.wikipedia.org/wiki/Distinguishing_coloring" class="extiw" title="en:Distinguishing coloring">distinguishing coloring</a> of a ring of six keys. Using two colors (here, red and uncolored) for the handles of the keys allows each key to be uniquely distinguished from the others by its position in the coloring.
<a href="//commons.wikimedia.org/wiki/User:David_Eppstein" class="mw-redirect" title="User:David Eppstein">David Eppstein</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>