6 Colors, 336 One-sided Squares

The pieces are made of magnetic foil with adhesive labels attached. Instead of six colors I used two different shapes and three colors. The pictures shows two 21x8 rectangles, which can be combined to get a 42x8 rectangle or a 21x16 one.

It's a good idea to sort the pieces before you start your construction.

A square ring of size 20x20-8x8 on a iron board of size 75cm x 75cm.

A square ring of size 19x19-5x5 is possible, too.