[-
  ($types, $colors, $defaults) = @param;

  foreach $type (@$types) {
    $flag = 0;
  
    foreach $color (@$colors) {
      $value = $fdat{$type . $color};
      $flag++ unless ($value =~ /^\d+$/ and $value >= 0 and $value < 256);
    }
  
    if ($flag) {
      # The user supplied an unacceptable value,
      # so use the default.
      delete $fdat{$type . $_} for (@$colors); 
      $hex{$type} = $defaults->{$type}
    }
    else {
      # User values were ok.
      $hex{$type} = 
        sprintf("%02X%02X%02X", map {$fdat{$type . $_}} @$colors);
    }
  }

  Execute({inputfile => "form.html", 
           param => [$types, $colors, \%hex]});
-]