For map (feature) services hosted on ArcGIS Online, only hollow- and solid-fill polygon symbology is effectively supported. Feature services can be published that use polygon hatching symbols, but the hatching will always be black--no color is supported. Similarly, when modifying the symbology of polygons in ArcGIS Online, only hollow- and solid-fill symbols are available. It would be very nice to support a more robust set of polygon symbology.