The flowers are a glistening bluish-lilac, erect, and ¾in. across when fully expanded.    From Wordnik.com.  [Hardy Perennials and Old Fashioned Flowers Describing the Most Desirable Plants, for Borders, Rockeries, and Shrubberies.] Reference

The usually bluish-lilac, sometimes pink or white flowers, borne in the axils of the upper leaves in whorls of three or four, form loose terminal spikes or clusters.    From Wordnik.com.  [Culinary Herbs: Their Cultivation Harvesting Curing and Uses] Reference