Danish Selig sofa, sure doesn't look like teak  

How about walnut?

I can't really tell what it is, but the catalog says oiled walnut. Now it is possible it was offered in other woods at other times....

All of the versions I have seen of this in real life have been walnut. It is not unusual for the seat frame to be made of beech that has a colored lacquer applied to make it look like walnut, since the frame is not very visible with the cushions in place so the manufacturer cut expenses by not making the seat frame of a premium wood.

Thanks Leif and tchp. The arm (second pic) looks too much like beech. I was able to grab some additional images. It does look like the back is for sure walnut.

Almost all, if not all, of those Kofod Larsen Selig chairs and sofas have the screwhead knockdown construction. If it is stained beech, then the wood on the inside of the keyhole opening will not be stained and be a light color (see attached example).
Also, in case you are interested, here are three Selig catalog pages for the chair and sofa versions of the design. As leif noted above, one of the pages lists oiled walnut as a wood option.

The seat frame is stained beech. The rest is walnut. They probably matched well when it was new. The piece of plywood on there is really classy.