No real need for a whole tutorial on it.
Usually you have some white to dark tint already applied to the the mesh, be it your vertex paint or an albedo.
Take the texture or paint, and multiply by the albedo texture so that the tips are whiter then the bottom.
Alernatively make a texture or pack one in a channel specifically for this.
The purpose is to have the bottoms of the blades significantly darker then the rest of the blade. This simulates the effect that a shadow would have without paying the cost for it.
Additionally, you can set 2 or 3 of the same mesh to different distsnces so that the near one has real shadows and a material without the darker effect, but the further one does not.