From the data plate the original interior upholstery color was 131 (Black MB-Tex).
If it were Palomino (AKA Date) it would be code 134.
https://www.w126-wiki.de/index.php?title=Lackierung_und_Polster#Polster
The interior was probably swapped out.
IIRC there may be a paper factory build sheet (with the color code) on the interior of the rear bench seat back.