While protein-based, natural human hair is easy to colour and holds dye easily, synthetic hairs, like those used in dolls, wigs, and hair pieces, is a bit harder to tint. Where store-bought hair dye kits fail, stronger synthetic inks work wonders on changing the colour of fake hair. Permanent marker ink, like that found in Sharpie pens, makes an effective, vivid, and easy-to-mix dye well-suited for this kind of colouring.
Put on rubber gloves; this will protect you from dyeing your hands while you work with the ink inside the marker.
Cut open the marker's plastic casing using wire snips. Cut off the very bottom of the casing, cutting slowly to avoid cutting the ink-soaked felt inside.
Remove the felt inside the marker using needle-nosed pliers.
Using a craft knife, slit the felt's plastic casing down the side, exposing the fibre and ink inside.
Repeat Steps 1 through 4 with the other markers you want to use; the more markers you include, the darker your colour will be.
Fill a spray bottle with rubbing alcohol. Leave about an inch of space at the top of the bottle to make room for the felts.
Place the marker felts inside the bottle of alcohol, and screw on the cap. Let soak for about an hour.
Mount the wig on a wig stand (note: the wig stand will likely get colour on it as well, so wrap it in cling film to avoid this).
Spray the wig with the spray bottle dye. If the bottle has a variable spray, use a fine mist. Coat the wig as completely as possible, then let it air-dry. Apply additional spray coats as needed.