It could also be just the lighting on that particular photo. In the other photos of the car it's hard to tell. It's definitely something to look into though. But as I stated before, if your buying a $400k + classic Porsche you better be paying an expert to go through the car. It would pretty to easy to tell if the tach isn't original in person.
Car is advertised on RL.
https://rennlist.com/forums/vehicle-marketplace/1057081-1996-porsche-993-carrera-3-8-rs.html