My favourite finish looks wise is red/garnet shellac. It has a beautiful, soft lustre, not overly shiny like a varnish. The colour of the shellac works well with the reddish/orange tones of osage.
For retaining the colour as much as possible, I think a paraffin wax coating alla Dean Torges is about the best I've come across. It also supposed to be the best at keeping out moisture. Maybe a water based varnish with a UV inhibitor would be another good option, but I don't know how durable the finish is to wear. Oil based finishes tend to accelerate the darkening of osage.
