Here's my Toelke Whip- riser is "dark" Cocobolo. It's like the wood is almost black with light streaks, but glows faint red in bright light..kinda like a smoldering piece of wood. The other side of the riser is a little lighter with more figure.
You might consider Bolivian Rosewood specifically. Or perhaps a wood with a red stain applied. Chechen, Sapele or Goncalo Alves with a stain would be interesting. If you're real picky you can have the bowyer take pics of the riser block wiped with alcohol to reveal what the wood will likely look like finished.
That Blacktail was nuts!!