In rug weaving, knots are created by looping yarn around pairs of warps and cutting off the standing end. The cut off ends of the knot become the pile, or the nap, of the rug. When looking at the rug from the "bottom" (where the rug was started), you are looking against the nap, with light being absorbed into the pile of the rug making it appear darker. When viewing from the "top," you are looking toward the nap, and the light is bouncing off the rug making it appear lighter. Often, these are referred to as the "dark side" and "light side" of the rug. Depending on the length of the nap, this change in color can be subtle or very drastic, but it is present in every handmade rug. 

There is no real right or wrong way to look at a rug, it is purely personal preference. When putting a rug on your floor, it is important to try looking at it from both directions. Depending on your space's particular lighting, one direction will instantly "look right."

It is simple to see the difference between the "light" and "dark" sides when comparing two identical rugs, first when viewing them each from opposite directions, and then when viewing them both from the same direction.

                                                                                                                                                                                                                                                                                                                                                                                  Opposite directions, showing the "light" vs."dark" sides         Same direction, both showing the "dark" side