uni_colour.xml

<?xml version="1.0" encoding="utf-8"?>
<Map background-color='#000000' srs="+init=epsg:3857">

  <Style name ="buildings">
    <Rule>
    <PolygonSymbolizer fill ="#CCCCCC"/>
    </Rule>
  </Style>

  <Style name ="buildings_border">
    <Rule>
    <LineSymbolizer stroke ="#555555" stroke-width="0.5"/>
    </Rule>
  </Style>

  <Style name ="road">
    <Rule>
    <LineSymbolizer stroke ="#171717" stroke-width="2" stroke-linecap="round"/>
    </Rule>
  </Style>

  <Style name ="landuse" comp-op="multiply">
    <Rule>
      <Filter>[fclass]='park' or [fclass]='cemetery' or [fclass]='forest' or [fclass]='meadow' </Filter>
      <PolygonSymbolizer fill="#125308" fill-opacity="0.8" />
    </Rule>
  </Style>

  <Style name="water">
    <Rule>
      <PolygonSymbolizer fill="#1b3442"/>
    </Rule>
  </Style>

<Style name="raster">
	<Rule>
		<RasterSymbolizer scaling="bilinear" opacity="1">
		</RasterSymbolizer>
	</Rule>
</Style>


<Layer name="rast" status="on" srs="+init=epsg:4326">
	<StyleName>raster</StyleName>
	<Datasource>
		<Parameter name="type">gdal</Parameter>
		<Parameter name="file">myGeoTIFF.tif</Parameter>
		<Parameter name="format">tiff</Parameter>
	</Datasource>
</Layer>


</Map>