I'm going to post here anyway despite the other thread:
1. Depending on the material, sometimes you can't get all the original color out. The more natural fiber (animal or vegetable) is in the original material, the easier it is to get the color out. Sometimes I use diluted bleach because it also helps weather material --although out course it can also totally destroy what you are bleaching if the bleach is too strong and you're not being careful -- and sometimes I use the color remover which reeks but works pretty well and there is much, much less danger of damaging the material.
2. When dying, add a handful of non-iodine salt (I get it at Walmart) to the dyebath and a good splash of vinegar. Both will help make the dye more colorfast.
3. Make sure you rinse the dyed material really, really well in progressively cooler water. I usually run it through the washing machine on cold/cold and then let it air dry to get the excess dye out. Otherwise, it could easily come out and stain either other clothes the figure is wearing or the body of the figure.
4. Beware that the color the dye claims to be and what it actually looks like (and I'm talking about when it is used to dye white cotton cloth) are two different things. For instance, when using RIT dye, the tan can be very green, the brown can be very purple, the denim blue is gray, the red can be very orange, you just have to do a lot of trial and error and learn how to mix the different shades to get what you want.
5. It is almost impossible to get something dyed a deep shade of black using something like RIT dye. You might think it is black when you take it out of the dye bath, but most of it will wash out. If you let it dry without rinsing enough, then you have the problem of stains.
6. If you want to go the natural route to darken things a bit and make them look properly worn, the tea or coffee dying can't be beat and is dead simple to do.