I would suggest putting this chunk into a routine. It provides some documentation, it becomes easier to modify behaviour in the future, because any changes are isolated within a short routine, and implementation details are separated from business logic.
use Readonly;
Readonly my %BGCOLOR => ( Extreme => 'red', ... );
Readonly my $DEFAULT_BGCOLOR => 'grey';
sub get_bg_color {
my ( $severity ) = @_;
return $DEFAULT_BGCOLOR
unless exists $BGCOLOR{$severity};
return$BGCOLOR{$severity};
}
my $bg = get_bg_color( $condition );
edit - corrected typo $BGCOLOR => %BGCOLOR; thanks, Anon Monk!
As Occam said: Entia non sunt multiplicanda praeter necessitatem.