If you were inclined to save bucks, I would think a repair on basically black, would turn out pretty well, and any subtle differences would become almost undetectable after a period. The upholsterer's smart, I don't think any wise upholsterer would provide a guarantee of a match (or fit) unless they were making all brand new seat covers. That's the kind of business where it's easy to get burned and I'm sure he (or she) has a few times. It's the kind of craft where customers under-appreciate the skill and amt of work it takes ..and variations between leathers. Especially if he's done high-end work like you say (wealthy people are notorious for not paying their bills and conniving how to get out of bills).
You might ask if he (or she) has a book of swatches, or any scrap black pieces around from previous jobs you could hold up and compare (and approve). If not, another option would be to consider some free swatches (online) to compare, and find what's acceptable.
Leather if cared for properly, can last a LONG time. It's possible the leather seat covers on your rig now could last 25 years with care. Not likely, but possible. But for the better bang, new pre-made seat covers probably make the most sense. Then you'd almost surely be set for the next 10 years and beyond, if you plan to keep it that long. I'm often tempted to do a repair that saves a few bucks but this might be one of those jobs where all new seat covers makes sense.
Sorry, just thinking out loud here.