use constant DS => 'my dsn here';

# later ...
my $dbh=DBI->connect(DS);
my($color1, $color2, $fontsize);
eval {
  my $sth=$dbh->prepare("SELECT color1, color2, fontsize, ... FROM prefs WHERE user_login=?");
  $sth->execute($login);
  $sth->bind_columns( \( $color1, $color2, $fontsize ) );
  $sth->fetch;
  $sth->finish; # using primary key to only fetch 1 row
};

if($@)
{
  print STDERR "Informative error message goes here with $@ for good measure\n";
}