[franciscop]

[spoiler alert]

I knew that 4 colours sufficed for any arbitrary map from back in the day when I learned this, but still I found it VERY rewarding by attempting to draw a map that needed 5 colors, and how intuitive this demo was for getting a "feel" for a thing that I knew only theoretically! Like I needed an impossible geometry to fit, either an area that stretched to a zero-width path (which would becomes a point, and thus 2 areas, so doesn't fit) or some other "impossible" geometry. Loved it, congrats on a really well executed idea!

[8organicbits]

It was really enjoyable to try. I got an optimal 4-color map on the first try, so I was over confident. My approach was something like: put a bunch of the 4-color maps next to a long Chile-like thing. When that didn't work I added borders until my device couldn't render it any longer. Very very fun.

[genewitch]

there has to be a layman's explanation. I knew the easiest way to get four colors was to put a split square inside another split square "donut", but the reason you can't force 5 colors is that word "inside". There has to be a nice, tidy "verbal proof" that no matter what, one or more colors will be "trapped" inside at most 3 other colors.

[waterproof]

You would think. The easier, five-color theorem proof fits in a few paragraphs but the four-color theorem really resists a simple explanation. Even the simplified 1990s version of the proof (which came ~20 years after the original proof and 100 years after the 5CT proof) required enumeration of hundreds of individual cases.

https://en.m.wikipedia.org/wiki/Four_color_theorem