Jaquard DeColourant, formerly called Discharge Paste, can be used to remove areas of color from dyed natural fabrics like cotton, silk, wool and linen. This is not bleach and does not weaken the integrity of the fabric like bleach can. Full instructions included on the jar.
Instructions: Apply with brush, stamp, sponge, applicator, stencil or screen print. Allow to dry, then iron on highest setting suited for the fabric type. For extra color removal, iron with steam. A heat gun may also be used, especially if the print is still damp. Color will leave at this stage. After color removal, wash fabric with Synthrapol or a mild detergent to return to natural softness.