WordNet sense 1 (exhibiting restrained good taste):

understated, unpretentious

WordNet sense 2 (having or showing or conforming to good taste):

tasteful

WordNet sense 3 (not showy or obtrusive):

restrained

WordNet sense 4 (not ostentatious):

unpretending

WordNet sense 5 (free from ostentation or pretension):

modest

WordNet sense 6 (marked by prudence or modesty and wise self-restraint):

discreet