Get your hands on Procion dye. The colors stay nice and bright for years. As they are very, very colorfast, you will need to take more precautions than you would with Rit (rubber gloves being the first of many). Something that works brilliantly well is to get squeeze bottles like the ones fast-food joints use for mustard and ketchup from a restaurant supply store. You get much better color control than just dipping, and don't have to make as much dye either. Simply squeeze an ample amount (really, really soak it!) on the area you want, and let the excess fall into a bucket. Of course, you can use a funnel to put the excess back in the bottle for re-use.
Darn it, now I'm getting an itching to do some tie-dye...
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