From a note on User talk:MrDolomite by User:DBD [1]

Just to let you know, the header for the PW template is red because the title originates in England – whereas Duke of Edinburgh is British, hence the same purple as the British Monarchs box, because that purple is a blend of red, for England, and blue, for Scotland DBD 01:59, 7 December 2007 (UTC)

— MrDolomite • Talk 03:08, 7 December 2007 (UTC)[reply]