Your client's a lucky guy to have chosen your services! Depending on the specific length required, I have had good experience with Allen Edmond's boot laces for my dressier boots. Could be worth checking out, if you were so inclined.
There are some pics buried in the Epaulet affiliate thread, but the answer is yes - Carmina kudu will darken with wear, and with any sort of conditioning treatment in general. I'm planning to use these as my beaters and accelerate the patination as much as I can!