Provide for good ventilation. If your laundry area has a window, open it. If not, open nearby doors and/or windows. Inhaling chemicals in a poorly ventilated space can prove toxic.
Apply bleach to clothing. You can spill or pour bleach, or use a dropper to apply it. Very quickly, unless your clothing is white or very light, you will start to see a reaction, as the color of the fabric begins to fade.
Observe the fabric over time. If you apply undiluted bleach to a dark fabric, you may notice the fabric is lighter after five minutes than it was upon application. In some cases, the bleach will continue to act on the fabric until it is devoid of color.