Steve
Mostly Harmless
Well, depends on how good the dye is, but there are some things you can do that will help.I mainly train in a black uniform. Does anyone have any tips to help prevent fading? They tend to go "grey" after a short time.
First, make sure you don't use any whiteners, ie, no bleach, no laundry soap that contains "whiteners".
Second, some people think that a vinegar soak sets the dye. I don't believe that, but I do love vinegar in a wash. That said, fixing the dye might help, I would just recommend an actual dye fixative, like this: http://www.dharmatrading.com/html/eng/1569-AA.shtml I've used this before, and it's awesome. It doesn't work on all dyes, but it works on most of them.
Third, turn the clothes inside out when you wash them. The friction of the wash can actually help fade the clothes.
Fourth, wash them cold and consider hang drying them.
Finally, if all else fails, consider dying them again. I have a tutorial on tub dying gis here: http://www.stevebjj.com/2012/01/18/how-to-dye-a-gia-step-by-step-guide/