I did this for Mac, but it was more difficult for the GTK images. Instead of using the implicit black for fill and stroke, you need to specify "currentColor". This will let the Inspector style the glyphs, specifically the navigation bar items that show up as blue when on/selected.
Created attachment 310491 [details]
Created attachment 310492 [details]
screenshot of before and after this fix
Comment on attachment 310491 [details]
Clearing flags on attachment: 310491
Committed r217039: <http://trac.webkit.org/changeset/217039>
All reviewed patches have been landed. Closing bug.