my $newfont = ...;

my ($fg, $bg) = (..., ...);

my $opt = "-fg => $fg, -bg => $bg";
$opt .= ", -font => $newfont" if length $newfont;

my $eval_string =  # note \$rw is escaped, $opt is NOT
qq{\$rw->Label(-text => "Col. 1", $opt, -padx => 10)->grid(
      \$rw->Label(-text => "Col. 2", $opt, -padx => 11),
      \$rw->Label(-text => "Col. 3", $opt, -padx => 11))
      };
print "eval string '$eval_string' \n" if $DEBUG;

my $rw = ...;  # tk object must exist before string is eval-ed

eval $eval_string;