This is an puzzle that I discovered in a book dating back to 1979 and found it to be very hard to solve.
The puzzle consists of sixteen tiles and each tile has a design in four colours.
In all, a total of six colours (green, purple, red, yellow, white and blue) have been used for the sixteen tiles.
To solve the puzzle you simply arrange the tiles so that blue always touches blue, green touches green, and so on until all the tiles match up.