First of all, welcome to LW.net. We're glad you found us.
Regarding your question, I've never produced a dye job of that type. But I'll give you some pointers on how I might go about trying, and let's hope that someone with more experience chimes in.
The first thing you'll need is plenty of scrap leather to try this out on. You never, ever, ever want to experiment on your final project. Ask me how I know this. I have a trash can full of "great" last-minute ideas.
Next, you'll need tan dye and black dye. I think my first try would be to dye the entire project tan, and use a wool dauber and the black dye to darken the edges. Then I'd use a very lightly-loaded dauber to produce the black streaks.
Maybe another way to accomplish this is to selectively apply a resist (like Satin Shene) to keep some areas lighter than others. I'm not very knowledgable in that area, so I'll leave it to someone else to expand upon that idea.
The most important thing is to get the two dyes and start experimenting on scrap. You may not be able to replicate that exact dye job, but who knows -- you may stumble onto something that looks even better to you.
Good luck! Let us know how it goes.