The hair in your hair system, unless it is made from virgin, uncolored hair (highly doubtful) is highly processed (bleached) and then dyed to the color required.
I am not sure what color you have now, but the darker it is, the hair will need to be bleached again, at best, you may get the color you want, but will seriously damage the hair. At worst it will destroy the hair, and you will be left with nothing.
It is always best practice to order the system in the color that you desire. The only deviation from this is for those who order a blond hairline, that will be dyed darker to avoid having to bleach the knots.
