I came across Marshall Squares™ on the Kadon Gamepuzzles website in January, 2007.
These are made with 5 colors, with at most 2 sharing a tile equally, and there are 25 of them.
An obvious arrangement of them is into a 5x5 square, with the
edges matching. That is quite difficult, as there are only 16
different ways to do it (not counting rotations, reflections, and color
See them HERE.
If we move the corner squares to centers of the edges,
as in the figure at the right, the task is much easier.
Then there are nearly fifteen hundred times as many ways
to fit the 25 squares together -- 23558 to be exact.
Here is a sample of them: