Comment 1 for bug 172151

i think so too. actually you only need 2 additional shapes as overlay.
both have no filling but the outline is colored. the first one has a white
color outline, the second one has a black color outline. and then you have
a gradiation from upper left to bottom right, where the transparency fades
down. the same in other direction for the black outlined shape.

and when you do this well, it kind of looks 3d. that could be a great
feature to make something like this automatically since you just need to
copy the basic shape twice, erase the filling color and change the outline
color.

play around a little bit and try to see what i want to say... :)