Simply washing will not remove all the dyes. The best way to remove dye for good is to let the fabric soak overnight in hot water and Synthrapol. Do not use Retayne - it will set the dyes. Synthrapol keeps the dye suspended in the water.
This blogger dyes her own fabrics and simply soaks them in hot water and detergent:
Part 1:
http://vickiwelsh.typepad.com/field_...d-fabrics.html
Part 2:
http://vickiwelsh.typepad.com/field_...ness-post.html