^^^^ I agree with 557.
My experience is wood (furniture, flooring, wood trim etc) darkens with light exposure.
It depends on the spicies. Pine is a good example. It is very light when milled and darkens to an orangy/red color. Maple basically stays the same. Oak can darken or lighten.
I don't know what is used for this wheel. It is probably European sourced. It isn't American walnut or maple.
The era in which the wheel was made puts the clear coat into the varnish class. It's not a urethane or a laquer.
Probably the best representation of the original is in the 67 aftermarket poster.
This is a picture of my Pantera's dash and console that I built for it. It is red oak with water based clear coat over it. It has not changed color since I built it.
Again. It's the species of wood and the base system used on the clearcoat.
I can't identify the wood used in the original wheel. It may be a variety of mahogany of which there are at least dozens of kinds depending on the location.
Mahogany is a tropical wood that would have a very wide grain pattern IF any at all. The way they layed out the wood, they wanted to minimize the grain pattern so it's difficult to read.