Remove all furniture from the room before getting started. You will need the access to the entire floor in order to ensure an even coloring when you dye the carpet.
Sweep up dirt and debris with a vacuum cleaner. Get into all the corners and edges around walls because that's a common place for dirt and dust to collect.
Wash the carpet with carpet shampoo. The polyester fibers in the carpet need to be clean in order for the pigments in the dye to adhere properly. Allow the carpet to dry completely before moving on.
Wear old clothing and put on latex gloves before handling carpet dye. The pigments in carpet dye are meant to be permanent and could ruin clothing and stain your skin.
Mix the dye with water in a spray bottle. You will need to read the instructions for the dye you bought to find the exact ratios. If you are dyeing a larger carpet and using a small spray bottle, you may wish to mix the dye in a bucket before pouring it into a spray bottle. This will ensure that the shade of the dye remains consistent across the entire room.
Spray the dye directly onto the carpet. Next, using a circular motion, rub the dye into the carpet and distribute the color evenly with a scrub brush. Stiff-bristled brushes work especially well for this. Start in one corner of the room and work in small sections until the entire floor is done.
Allow the dye to dry completely before walking on the floor or returning furniture. If anything touches the floor before the dye has been fully absorbed it could easily be transferred, damaging your furniture.