Thanks Lazur!
Yes, I did follow your thinking about using the voronoi pattern like turbulence, as part of a filter. I just haven't had a chance to read Tav's tutorials, and learn how to make custom filters yet. Plus, Inkscape doesn't have such a thing, does it? Might be nice feature request!
I'm pretty happy about how it came out. Of course if you zoom in to the svg, it gets ugly pretty fast. While with using filters, zooming doesn't show those things, as much. But at face value, I'm satisfied.
The biggest lesson I learned about the gradient mesh, is that you can spend all day tweaking the node/stop colors. After a certain point, you just have to call it good enough. I was expecting it to be much easier than it turned out to be. But maybe with some experience, it will become easier.
I was surprised that it can't provide nearly as much detail as I was expecting. It looks like you can't get any more than 20 lines and column of nodes/stops. For a small object, yes, you could get a lot of details. But for even a medium sized object as this leaf, I was wanting more.
I used 20 x 20 in the main leaf color. Because there's thin, dark outline in the photo, I used a stroke object, but only 12 x 12 on that mesh. Probably I could have tweaked that one a little better. I don't remember if it was 12 or 20 for the veins, but the veins have a mesh too. And the stem (petiole) too (something like 4 x 10). Probably could have tweaked it a little better too.
I was also surprised that I didn't run into more performance issues. I think comparing the gradient mesh, to my usual reaslism style (many small, blurred objects), I don't have nearly as much trouble with slowing and crashing. I really only ran into trouble when I added the voronoi pattern, which I converted to paths.....maybe didn't need to convert to paths??? And especially after I duplicated it. Just those 2 objects added a MB to the file!