I'll just add to the above by saying that creme peroxide (also known as developer) is the active agent in the dying process and prepares the hair to accept the dye. ie, strips the hair & makes it porous.
The percentage of the peroxide indicates its strength.

If you're just changing your hair colour to a few shades darker, then you only need a 4% or 6%.
Dramatic changes can mean using a higher strength right up to 12%.
Most off-the-shelf home dyes have a 12%.
Because replacement hair has already been process & stripped & dyed, it is much more susceptible to absorbing colour than your own natural hair would be, it will dye faster & deeper.

Like Paul, I dye my hair using tubes of professional hairdressing dyes.
I use the same colour on my replacement & natural hair.
But I mix up 2 batches.
The replacement hair has a 2% creme peroxide developer & 12% for my own hair.

Because different lighting brings out different tones in hair, I really wouldn't recommend store bought dyes. They often have brassy tints in them where as the professional dyes have a much wider range of colours & more subtle shades.

You can buy them on-line or from places like Sally's, worldwide.

I'm only referring to percentages above.
For details & info re Vols (seen on creme peroxide bottles) read:
http://www.using-hydrogen-peroxide.com/h...oxide.html


I hope this info helps someone.