Behdad and I spend a few minutes tracking down a problem
where color glyphs in GTK+ entries will sometimes fail to render.

The relevant GTK+ bugs are here:
https://bugzilla.gnome.org/show_bug.cgi?id=788071
https://bugzilla.gnome.org/show_bug.cgi?id=790255

I've pushed the fix here: 
https://github.com/matthiasclasen/cairo/commit/75d6c90578926e7cea0c9c286100cc8b2f4be460