Our friends in São Paulo gave our daughter these cute wooden folding toys. They’ve got elastic running through the middle, so you can twist the pieces around and make different shapes. After playing with them for a while, I noticed that they have an interesting mathematical property: when folded into any flat shape, any two triangles that meet are always the same color, forming a grid of diamonds (or squares, depending on your point of view.) I can’t help wondering why this is. It has something to do with the repeating pattern of four colors, obviously, but what?