However, if another colour is chosen and the properties box OK'd, when returning to this option, in the case of pedigree lines and union lines the 'Automatic' option has disappeared:
The only way to get the option back is to delete the object and start again. This does not happen with any of the colour choices for an individual - is this because you can set the defaults for the gender symbols in File|Properties|Automatic/Default?
The problem comes when you change the Relation (eg from Marriage to Divorce) or Pedigree Link (eg from Biological Child to Adopted Child) type and want to use the default colours for the lines - they are not available unless you match the colours by eye.