The colors of boundaries of the mass have been changed at random.
The color of the boundary in an upper and lower, right and left all sides has been changed at random.
If the sizes of the mass eyes are reduced, the square of the mass is abstracted and becomes as a whole one pattern.
The impression changes greatly when the boundary is made fat.
When the width of each border line in an upper and lower, right and left all sides is changed at random.
The expression changes further when the lines are made bold.