That's an extremely interesting idea. You could have a "fill" tool with "select texture" allowing all manner of textures in addition to the color options. You could take a cloudy sky image and use it as a texture, for instance, or a grassy field texture. color options could include all the current colors, metalic or not, and transparency. it might not be hard to add such a tool, although being not a programmer I don't know, LOL. You could, for instance, make a layer with a straight solid pencil line across it, fill the top with sky full of clouds (blue over white ground) and the bottom with grass (maybe several fills of different shades would create a nice field) then that could be your bottom layer letting you lay in a landscape over top.
I really do too many "pastoral" landscape starts. LOL
Using HP touchsmart tx2 1020ao tablet laptop with stylus and multitouch screen. I love being able to draw right onto my computer! Now if Art Rage had a "fingerpaint" mode I'd really be playing!