For anyone wishing to help me fix icons, here is the trick: apparently
GTK+ would fill the paths with CSS colors, not stroke them. So when we
have icon drawing based on path-stroking, they don't end up as expected.
In Inkscape, just run "Stroke to Path" to transform a stroke design in a
fill design.
I am fixing "gimp-tool-cage", "document-revert", "gimp-image-reload",
"gimp-reset" and "view-refresh". More to follow as we discover them, I
guess.