There's a variety of shades/finishes in the red guts too. The dash metal, column, column door, didn't exactly match anything else. Even though the pigment mix is very close to the same, the different finishes dry to slightly different shades. Then how light reflects changes how the color looks to our eyes even more. Glossy sanded to flat, water or oil on flat are good examples of the light effects.
So the dash cap in my 67 metallic red didn't exactly spot on match the seat skins. It's mighty darn close. A slight difference in that vinyl's grain that vinyl being heated/stretched/formed over the pad have to be the factors.
For what its worth, my red drivers seat has a very well worn panel nearest drivers door. That one area will at times closely matches the dash metal. A little armorall will bring its appearance back closer the dash cap and the rest of the seat.