Regardless if you grow bearded, Siberian, spuria, Japanese, Louisiana, dwarf Dutch or sweet flag iris, it is the array of flower colors that draw the eye. Petal color options, either solid or bi-colored, bring the opportunity to group iris plants for vivid and stunning displays. Focus on contrast when mixing irises that bear different flower colors. This contrast heightens each flower's color and shape. Avoid planting irises that bloom in the same color next to each other as you risk "washing out" the effect of their color and diminishing the subtle tints and shades of that color.
Search out the general flower color for each iris plant in your collection. Look on plant labels that accompanied the plant rhizomes from the nursery or look up their variety names in perennial books, catalogs or online to glean their expected flower color.
Stick a small dot or other sticker on the dry leaf of the iris to help you quickly identify its general flower color. Chances are you are transplanting irises in late summer when they are not in flower. For example, any light blue flowering plant should get similarly coded stickers different from other plants that may bloom white, yellow, dark purple or bi-color.
Plant irises with contrasting colors next to each other in the planting bed. For example, if you plant a purple flowering iris, nearby irises should have white, yellow or orange blooms. If the iris is bi-colored, match one of the petal colors with a nearby iris. For example, if the bi-colored iris is yellow and purple, plant it next to solid-color purple or yellow flowers.
Use white or pastel colored iris to unify large collections of plants that may all be similarly blue or purple. This also pertains to green-leaf and variegated leaf iris plants. Planting the occasional white or pale iris flower will contrast the darker flowering irises and supply a color reference to help visually differentiate among all the tones. A variegated leaf iris that randomly occurs among many solid green leaved types is more visually punctuated.