User:EdLoach/JOSMPostcodes

Save the content below as postcodes.xml on your local drive and add it using the Map Paint dialog in Preferences.

<rules name="Postcode Highlighter"
      description="Highlights addressed properties with/without postcodes"
      version="0.1_2011-05-17"
      author="EdLoach"
      shortdescription="Missing Postcode highlighting">
 <rule>
   <condition k="addr:housenumber"/>
   <area colour="house#f807f8A0" priority="-10000"/>
 </rule>
 <rule>
   <condition k="addr:housename"/>
   <area colour="house#f807f8A0" priority="-10000"/>
 </rule>
 <rule>
   <condition k="addr:housenumber"/>
   <condition k="addr:postcode"/>
   <area colour="postcodedhouse#00da8bA0" priority="-9000"/>
 </rule>
 <rule>
   <condition k="addr:housename"/>
   <condition k="addr:postcode"/>
   <area colour="postcodedhouse#00da8bA0" priority="-9000"/>
 </rule>
</rules>