ALPHA VERSION, LIKELY STILL HAS ERRORS; USE AT YOUR OWN RISK
For use with tilesets created using the base tiles in
https://inkscape.org/~apmbcn/%E2%98%85two-level-isometric-tiles-with-30-degree-slopes
and
https://inkscape.org/~apmbcn/%E2%98%85two-level-isometric-floor-and-wall-tiles-with-30-degree-slopes
These masks are meant to create shade for the various floors and walls of the tiles. The tile matching each shading mask is indicated outside the svg file's page. Place these in your game as objects on top of your tiles and adjust their alpha to create the desired level of shading. Using this method, the borders of the tiles will never be shaded, only the interiors will be. This is intentional, as the inner borders of the tiles should have the same color.