Colour glyphs using the SVG tables are SVG documents embedded instead of vector glyphs, using tables designed by Mozilla and Adobe. FreeType only supports extracting the document as a blob. Also, unfortunately, Pillow does not support parsing&rendering SVG documents either.

Supporting this format would require an SVG parser (though I believe it is a slightly more constrained subset than the full SVG spec), plus wiring all that up to an Agg renderer. This is likely far too much work for us, but maybe if someone is motivated enough to do so...