Check what kind of carpet you have. Cotton, linen, or natural blends of up to 60 percent all work with Rit dye, but all-synthetic fibers or blends with more than 50 percent polyester content, the dye will not work. If you aren't sure what kind of carpet you have, try to find the brand and color name, and check with your local flooring store.
Put on rubber gloves to protect your hands, and then use trash can liners to cover the area around the spot that is to be dyed. If the spot is small, try laying a liner on top of it and then cutting a hole the exact size of the spot to be treated. Then use electrical tape to secure the liner.
Use a color-removing solution to get rid of your carpet's faded color. Instructions for these products can vary, so consult the label for exact color removing instructions.
Get out a medium bucket and pour 2 tablespoons Rit liquid dye into 1/2 cup of very hot tap water. Make sure to mix thoroughly.
Dip a clean rag in the dye and then pat the spot gently with the rag. The dye will transfer from the rag into the carpet. Continue to blot the area until you achieve the desired color. Then throw the rag away. Wait 20 minutes for the dye to set, and then remove the trash can liners from the floor.