Ok, assuming I got the translation correctly, I have some questions:
1. When you order the hairpiece, do you ask for a color match to your un-dyed hair samples ?, it seems that by doing this you are shooting your leg, because the dye that you will use to dye your hair (and 1" of the hairpiece), will not give the exact same color as your original hair samples...
2. Why not dye the entire wig's hair ?, why just 1" ???

You colour the 1" of the hairpiece and your own natural hair only were they meet, BECAUSE you dont want a complete uniform colour as like you said there are a mixture of colours in natural growing hair and leaving the top slightly lighter gives it that more natural contrast. Were the hairpiece meets the natural growing hair you fade the colour up like I said approx 1"
Do it like in the graph below and nobody can tell any colour discrepancy because you have the colour fading creating an illusion to the human eyes * Fading the colour is the key *

Heres what I mean :