Also represent colorize-alpha at style level (currently unused by carto)
Also represent colorize-alpha at style level (currently unused by carto)

mojodna/mapnik-reference,florianf/mapnik-reference,CartoDB/mapnik-reference,mapycz/mapnik-reference,mapnik/mapnik-reference,florianf/mapnik-reference,gravitystorm/mapnik-reference,gravitystorm/mapnik-reference,mojodna/mapnik-reference,mapnik/mapnik-reference,mapycz/mapnik-reference,CartoDB/mapnik-reference,mapnik/mapnik-reference