relationship an interference pattern or moire effect can result when a non woven fabric is used for the vane material the problem of a moire effect in the window covering when it is closed is avoided in some instances however it may be desirable to use a woven or knit material for the vane material a basic woven material will give a moire effect because this type of material has a very ordered orthogonal surface structure to avoid a moire effect when the window covering having a woven or knit vane material is in the closed position a crepe woven material can be used as the vane material because crepe woven materials have a much more randomly oriented surface structure alternatively the surface of the woven or knit material can be altered to randomize the surface fibers for example by sanding napping or calendarizing window coverings having first and second sheer fabrics and vanes of various colors and combinations of colors are contemplated within the scope of the present invention for example to provide a more transparent window covering in the open position dark sheer material can be used for the first and second sheer fabrics because dark colors reflect less light than lighter colors similarly white or light colored sheer materials provide a more translucent effect when the window covering is open the vanes may be the same color or a different color than.