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Because acid dyes don't have other types of dyes mixed into them (like an all-purpose dye does), the color you'll get at the end of the dyeing process will closely match the color you chose. Depending on what color of dye you want, you may need to special order it online from a dye company. The exception to the rule about color-matching is if you were to try and mix together 2 different shades of acid dyes. Each dye has multiple pigments that could mix with pigments from another dye and change the outcome of the color to be different than expected; the results might be slight but it also could be dramatic. If you want to do this, test the mixed dyes on a piece of scrap nylon first. All-purpose dyes can be found at most craft and grocery stores, making them great options for times when you don't want to wait for a special order to come in. The color of your nylon might be slightly different than what's on the box because all-purpose dyes include 2 types of dye: a direct dye for cotton and a leveling-acid dye for wool/nylon. Only the leveling-acid dye will affect your nylon. While the color won't be exact, it will still be very close to what's on the box or label. Just keep in mind that there might be a slight difference, especially if you're trying to match your nylon to the color of something else (like a pair of pantyhose with your favorite red lipstick). Apart from the basic colors you might get in something like an egg-dyeing kit, there are tons of other colors available at craft stores, grocery stores, and online. You'll need about 10 drops of food coloring for each item you want to dye unless they exceed 1 pound (use fewer drops for a lighter color or more drops for a more vibrant shade). You could also use natural food extracts, like beet extract for red dye, turmeric for yellow dye, and spinach juice for green dye. Ideally, use a powdered drink mix that is completely free of sugar and sugar-substitutes; otherwise, the nylon will turn into a gunky mess. Plan on using 1 packet of drink mix for each item under 1 pound that you want to dye. The great thing about using a drink mix on nylon is that the color won't wash out when you clean it like it would if you used it on cotton.
Use an acid dye to get a color that closely matches that of the packet. Choose an all-purpose dye for an easy-to-find dyeing option. Opt for food coloring for a wide array of colors to choose from. Pick an unsweetened powdered drink mix for an inexpensive option.