1.Gray plants(ex. Artemisia lactiflora brings brighter colors into relief..
2.Mauves and blues like contrasts put next to yellow
3.Strong yellows go best next to bronzes..
4.Reds--oranges-- and bright yellows bring things close
5.Blues give an effect of distance

Good Color Dividers:(create interest also)
1.White flowering plants--Shasta daisies--cimicifuga racemosa-- white geraniums used for separating bright colors--use with caution
2.Perennials with distinctive foliage and form good dividers--Bearded Iris--Artemisia
3.Appearance and outline--(shape of bloom) in ones combo's (ex.) bulky--round outline of lupins against spiky habits of delphiniums or (pink and yellow lupins with Weigela Praecox Variegata ' Christopher Lloyd's garden) contributes as much interest as color scheme..