Here are two very similar shades of Dianas, but as you can see they're not exactly alike:
On the left is a 3 series Diana from 1994-1996, and on the right is an older 0 series Diana from 1986-1988.
Both of these are taupe, but as you can see here they are not the same shade. Why would the color be different even though both are taupe shades?
Evolution of lambskin manufacturing over time
Well for one, materials, both being lambskin, have drastically changed in manufacturing process and also technology has changed over this period as well.
When you get a style that is so iconic that has been produced over the period of 6-7 years, inevitably technologies and manufacturing processes will change.
And that is why one of the most interesting parts about my job is identifying and sourcing those specific colors for you.