That looks amazing - what's their process for colour matching? I desperately need about four Kelly straps!
They might be able to help with color matching but I didn't ask. I'd simply selected the leather color myself by calling up the leather color samples online from their website and comparing it to my purse - holding them both side by side. Also chose the width (0.75") and length of the strap, and type of buckles (Nickle #16). I also made sure they know what color thread to use and how I want it to be sewn to be as similar to the original as possible with the ends sewn up.
Glad to also know that the colors online matches very closely to how it would appear IRL.
The width I'd selected is a bit wider than the Kelly strap but more comfortable on the shoulder as I found my Kelly strap bit into my shoulder quite a lot if I load up the purse. Good luck if you do decide to customize it.