Mesh consist of variety of points and tangents. Each point may be colored to specific color, smoothness of color transition may be adjusted with tangents for each separate point. That way this tool allows to create complicated realistic vector images.
Mesh fill is poorly realized in Adobe Illustrator (lack of instruments and settings)
This is why Mesh Tormentor plugin is widely used. (plugin is free).
3. Draw additional lines to divide an object. Each vertical line need to be crossed with each horizontal line. Horizontal lines can’t cross each other, the same as vertical lines can’t cross each other. Lines should be placed at main light – shadow changing edges. If there are small details – draw more lines and place them closer to each other.
4. Use option Divide in Pathfinder tool to cut main shape with previously created lines. Now we’ve got a bunch of separate shapes.
5. Color all the objects with random fill color and make no-stroke mode. Click “Make One Cell Mesh Based On Path” in Mesh Tormentor.
Now we’ve got a bunch of separate mesh objects.
6. Start sewing separate mesh objects into one with “Sew Docked Meshes” Mesh Tormentor Tool. You need to pay attention to Corner Nod Point placement. If Nods are placed in wrong way – it would be impossible to sew on separate meshes into one.
8. After Fixing all wrong corner nods and sewing all the elements to one mesh we can use “Capture color from raster object to all selected meshes” option to color illustration. To do this place raster image reference directly under the created mesh object. Then select both and click “Capture color from raster object to all selected meshes” button in mesh tormentor. Enjoy the magic! (of course coloring of some mesh points need to be fixed, but it is a small thing ).