community of dyers

The best method is to use sodium dithionite (aka sodium hydrosulfite), but even that will not work on all dyes. It works best when used at high temperatures, i.e. on the stovetop. Dylon Run-Away does contain this chemical, but is it as strong as Rit Color Remover? I'm not sure. Did you use it on the stovetop? If not, you could try again on the stovetop, because it's much more effective then than at room temperature. Soaking in sufficiently hot water will also in itself help to remove some of the Rit dye, since it is not very strongly attached to the fiber.

Here is the Rit Color Remover recipe, from the inside of the box:

"Stove-top method. Wash items as usual. Do not dry. Fill large stainless steel or porcelain enamel pot (not aluminum or non-stick) with water, allowing room for items. Heat water to simmer [190°F or 87°C]. Carefully add Color Remover, pouring just above water level. (AVOID BREATHING DUST. USE WITH ADEQUATE VENTILATION.) Stir to dissolve thoroughly. Carefully add wet items (avoid crowding); stir continuously with a long-handled spoon or stick, 10 to 30 minutes so color will be evenly removed. DO NOT BOIL. Carefully drain solution into sink. Using rubber gloves, thoroughly rinse items, first in hot water, then in warm water (RINSING IMMEDIATELY IN COLD WATER MAY SET CREASES). Squeeze gently to remove excess water. Rewash items with detergent."

But the thing is, even using Color Remover in the most ideal fashion will not always work. Some dyes are dischargeable (the process of decolorizing dye is called discharge), while others are not. Some dyes will stubbornly retain their color no matter what you do to remove it. (See What chemicals can be used to remove dye?.)

Dyeing may be problematic, as well, because the dots of color will always end up darker than the rest of the garment. Obviously, though, they must be far less obvious on a purple dress than on a white one. A dark color will cover dots and splotches better than a light one, and low water immersion dyeing will do an even better job of disguise.

I must insert my usual warning against using Rit dye. It is an all purpose dye, which means that it runs in the laundry every time you wash it, fading quickly and ruining other clothes. It's much better, if you're dyeing cotton, to use a higher quality dye such as Procion MX fiber reactive dye; surprisingly, this dye is far cheaper than Rit dye, if you're going to be dyeing more than a single garment, and yet it stays bright years longer, produces more reliable colors, and is much easier to apply since it does not require hot water.

However, if you must use all-purpose dye such as Rit, you can get acceptable laundry performance if you after-fix it with a cationic dye fixative such as Retayne. Note that neither salt nor vinegar will help to fix Rit dye at all; only the special dye fixatives will work. Of course, your local store will rarely carry such a thing. Sometimes Joann's Fabrics has Retayne, but usually it is necessary to mail-order this product.