The Interlocking Chain quilt block, a seven patch design, features only squares and half square triangles to achieve this "optical illusion" block.

The quilt layout featured below on the left sets the blocks on point with large, corner triangles on each block. The different colour placement of these large triangles forms a sort of "colour blocking" effect in the resultant quilt.

The quilt layout illustrated on the right also sets both whole and half blocks on point and separates them with sashing strips to further enhance the colour choices. This creates a look of "plaid" in the quilt -- at least to my eyes.

Check out other "optical illusion" blocks:
~ Folded Corners
~ Formal Frame
~ Garden Square
~ Plaited Block
~ Ribbon Star
~ Twisted Ribbon