Inkscape layer compatibility
This change makes the SVG invalid in Illustrator (v 17.0.0).

This is an example of the kind of issues I referred to in #2 about ongoing problems between SVG compatibility between Inkscape and files created in Illustrator. Unless this file can be changed in a way that maintains compatibility (and editability) with Illustrator, I’m unfortunately not prepared to merge in the change. I’m sorry about that, but if I’m going to maintain this, I need to make sure my tools work. Until that happens, you’ll need to use the workaround I described in #2 to view the light background version of this file.
I don't know if this will work, I don't use this propitiatory vector graphics editor.
Alternative solution since layers are not officially supported, you could split the layers.