Unfortunately dyeing with natural dyes is not as simple as using a fiber reactive dyes. To truley have your natural dye fix and washfast you must use a mordant(vinegar will not work). The mordant you want to use depends on the dye you are using and the color you want to achieve. Most mordants are metal salts, like alum and tin. Pretty safe when used with caution so exposure(especially inhalation) is minimized, same holds true for fiber reactive dyes.
To do traditional-type tie-dyeing done with direct application, folding and binding the fabric and applying a variety of colors you need to be free of having to boil your item for the dye to set. Natural dyeing requires a style of dyeing called immersion, usually in a hot dye bath. However, you can still create resists by binding your item and then dyeing it. Furthermore, you can add color by overdyeing your item after you have rinsed it from the first dye bath.
Just be aware that if you use some recipes out there that tell you to use vinegar to set your dye(whether it be onions, berries etc.) your colors will not be washfast. You will essentially be "staining" your item.Aurora Silk
Have some good info.