Basil Dark Opal : Ocimum Basilicum Dark Opal Basil . This basil plant produces beautiful deep purple leaves that retain their color all season. Leaves are very fragrant and tasty. Great as a garnish, in salads, and to make flavored vinegars. Grown as much for its ornamental and landscape garden value as for its culinary value. Plant growes 12 to 24" tall and is a annual. Dark Opal basil was introduced in Connecticut in the 1950s.