i love this red-brown tabac/sienna. 07 saw some good leathers. i kept going back to this colour last year but i settled for 06 cognac as i'd wanted a tan shade and i was a bit hesitant about wardrobe possibilities with a red-brown. it would go perfect with greys, greens and blues, just to name a few.
Sienna goes with a whole lot of neutrals. I wear a lot of bright colours so I do have some trouble with my Sienna Day but the leather is TDF so I constantly wear neutrals just so I can carry my Sienna.