Reference:Square Pattern

	The square pattern is a block pattern that generates a repeating pattern of squares in the x-z plane. In this instance imagine tall rods that are square in shape and are parallel to the y-axis and grouped in bundles like shown in the example image. Four separate colors should be specified as follows:
The square pattern.

pigment {
  square [COLOR_1 [, COLOR_2 [, COLOR_3 [, COLOR_4]]]]
  [PATTERN_MODIFIERS...]
  }

Each side of the square is one unit long. The square rods of color extend infinitely in the +y and -y directions. If no colors are specified then default blue, green, red and yellow colors are used.

You may also use pigment statements in place of the colors. For example:

pigment {
  square  
  pigment { Aquamarine },
  pigment { Turquoise },
  pigment { Sienna },
  pigment { SkyBlue }
}

When used with textures, the syntax is...

texture {
  square  
  texture{ T_Wood1 },
  texture{ T_Wood2 },
  texture{ T_Wood4 },
  texture{ T_Wood8 }
}

The square pattern has a default color map built in that results in red, blue, yellow and green tiles.

This is a block pattern so, use of wave types, color_map, or slope_map modifiers is not allowed.