choosing fabrics  

I can think of a dizzying list of appropriate colors:
beige, off-white, ecru, cream, oatmeal, tan, sand, fawn, biscuit, buff, or even mushroom.
Yes, I'm a fan of "boring" upholstery, particularly where there's a wood frame involved. It shows off the design nicely, doesn't compete with the wood, you'll never tire of it, and it's easy to resell.
You want color? That's what throw pillows and rugs are for.

I agree
I'd go with a tan or cream color that has a yellow-ish undertone, it will highlight the warm tones of the wood.

I'd also go for a...
I'd also go for a yellow-tone, or maybe a nice green?

a tan or beige was my first...
a tan or beige was my first choice to.
the suggestion of a yellow undertone hadn't come to mind,
but definitly appeals to me.
thanks claus for the pictures, do you know the designer of the last chair?

Finn Juhl, Diplomat chair.
Finn Juhl, Diplomat chair.

I thought so.
the armrests...
I thought so.
the armrests have exactly the same flares as the ones on my chairs above.
but I assume Juhl had nothing to do with my chairs.

neutrals
I would go with neutrals for all the reasons above.
Warm gray also looks really great with rosewood.