collection of online and printable map activities for kids and adults. At the bottom of that collection was a link to Mathigon's map coloring challenge. The challenge is to use as few colors as possible to color in all 50 U.S. states without the same color touching two states at the same time. For example, if I color New Hampshire purple, I can't use purple on Vermont, Maine, New York, or Massachusetts but I could use purple on Pennsylvania.
Mathigon's map coloring challenge can be completed online where they offer the same challenge for coloring maps of South America, England, and Germany. But if you send your students to that page they'll be able to quickly click to see the solution to the challenge. So what I'd do instead is print a blank map from a site like Printable World Map then have students try the challenge. Another option would be to upload an outline map to a service like Google's Jamboard to color the map online. Watch my video below to learn how that process works.