As vector drawings are based on different objects, that each have their own set of properties (i.e. 'brown fill, black stroke') - no, this is how it works.
You can use blur and gradients for shading, and you can use the bucket tool to automatically fill areas (beware, it's not a very exact tool).
For the black/green outlines, another approach would be to use the PowerStroke Path effect.
For tracing, you could also use the autotrace feature in Path -> Trace bitmap. Be sure to go through the tutorial in Help -> Tutorials -> Tracing, if you want to understand the dialog's options.