When colors run or "bleed" in the laundry, it means that some of the dye from darker garments has transferred to lighter colors. The result is discoloration that can range from slight to extreme. Once color bleeding occurs, there's not much you can do to correct it, and often the affected garments need to be thrown out. However, there are several things you can do to prevent color bleeding from occurring in the first place.
Sort your laundry into dark colors, light colors and whites. This reduces the chance for darker colors to run onto light colors, and is the most important step in the war against bleeding colors.
Wash new clothes by themselves. If you have recently bought new clothes, they may have extra dye or may not be set correctly. Some even have a warning label detailing special laundry care for the first wash. Take precautions by always washing new clothes separately the first time they are washed.
Soak dark or new clothes in salty water for half an hour. The salty water helps the dye "set," which keeps it on your clothes instead of in the wash water.
Soften your water with white vinegar. Hard water transfers colors in the wash more easily, but it is easy to soften the water with 1/2 cup of vinegar every time you wash.
Use "color catching" products. These products are sold at most grocery stores and absorb dyes that are released in the wash before they can be transferred to other garments.