Starting with QGIS 2.4 we have seen the introduction of both shapeburst fills and inverse fills. This allows for some great visualizations.

Options:

QGIS Layer Style File (save it as a “.qml” file and load a style):

<!DOCTYPE qgis PUBLIC 'http://mrcc.com/qgis.dtd' 'SYSTEM'>
<qgis version="2.4.0-Chugiak" minimumScale="0" maximumScale="1e+08" simplifyDrawingHints="0" minLabelScale="0" maxLabelScale="1e+08" simplifyDrawingTol="1" simplifyMaxScale="1" hasScaleBasedVisibilityFlag="0" simplifyLocal="0" scaleBasedLabelVisibilityFlag="0">
  <renderer-v2 preprocessing="0" type="invertedPolygonRenderer">
    <renderer-v2 symbollevels="0" type="singleSymbol">
      <symbols>
        <symbol alpha="1" type="fill" name="0">
          <layer pass="0" class="ShapeburstFill" locked="0">
            <prop k="blur_radius" v="7"/>
            <prop k="color1" v="0,0,255,255"/>
            <prop k="color2" v="0,255,0,255"/>
            <prop k="color_type" v="0"/>
            <prop k="discrete" v="0"/>
            <prop k="distance_map_unit_scale" v="0,0"/>
            <prop k="distance_unit" v="MM"/>
            <prop k="ignore_rings" v="0"/>
            <prop k="max_distance" v="5"/>
            <prop k="offset" v="0,0"/>
            <prop k="offset_map_unit_scale" v="0,0"/>
            <prop k="offset_unit" v="MM"/>
            <prop k="shapeburst_color" v="26,194,203,255"/>
            <prop k="shapeburst_color2" v="255,255,255,255"/>
            <prop k="use_whole_shape" v="0"/>
          </layer>
        </symbol>
      </symbols>
      <rotation/>
      <sizescale scalemethod="area"/>
    </renderer-v2>
  </renderer-v2>
  <blendMode>0</blendMode>
  <featureBlendMode>0</featureBlendMode>
  <layerTransparency>0</layerTransparency>
  <label>0</label>
  <editforminit></editforminit>
  <featformsuppress>0</featformsuppress>
  <editorlayout>generatedlayout</editorlayout>
  <excludeAttributesWMS/>
  <excludeAttributesWFS/>
  <attributeactions/>
</qgis>