The Tartan Cube uses only four colours to distinguish all possible cube positions.
The Tartan Cube is a Super Cube design, as it shows the orientation of the side parts. Thus it has 2048 times more possible positions than a regular Rubik's Cube.
This cube is very hard to solve, because all faces look very similar.
For more informations about this design, see Dan Hoey's post in the Cube Lovers archive.
Tip: To get a nice effect, apply the Pons Asinorum pattern to this cube.