The Collaborative International Dictionary of English v.0.48:

Bluets \Blu"ets\, n. [F. bluet, bleuet, dim. of bleu blue. See
   Blue, a.] (Bot.)
   A name given to several different species of plants having
   blue flowers, as the Houstonia c[oe]rulea, the Centaurea
   cyanus or bluebottle, and the Vaccinium angustifolium.
   [1913 Webster]