When I was at a place called Woodworkers Source today, I noticed BEHLEN Master Solar-Lux alcohol based stain is available in at least 8 different wood colors as well as Red, Yellow, Green and Blue.
The Mahogony is available in 3 different colors, one rather brown, one very red and one which is purpleish.
If your applying one of these stains to Walnut, you should do some experimenting because they all will darken the wood.
If you can't find these stains, most woodworkers stores will have something similar.