while it has been extensively proven that any 2D map can be colored with at most 4 colors, has any hypothesized why that is (outside the computer programmed brute force method)?
I think I can see it just by doodling.Sketch a map with three regions and needing three colours.The shapes and sizes of the regions and the overlap borders are irrelevant. Now add a fourth region which borders the first three regions and you will see that this fourth region must completely surround at least one of the other three regions.