Roses exhibit a remarkable spectrum of colors, resulting from centuries of selective breeding and cultivation. The genus Rosa comprises over 300 wild species, but thousands of hybrid varieties showcase a vast and diverse palette. This wide array of hues is due to the plant’s natural ability to produce specific pigments.
The Primary Color Palette
The foundational colors—red, pink, white, and yellow—are determined by two main classes of pigments. Red and pink hues are derived from water-soluble anthocyanins, while yellow is created by fat-soluble carotenoids. The intensity of these primary colors is highly variable, allowing for a wide range of shades.
Red roses, the classic symbol of passion, range from light scarlet to rich, almost black crimson. These colors are produced by high concentrations of specific anthocyanins. Pink roses, which convey admiration, represent a softer expression of the same pigments at lower concentrations.
Yellow roses, associated with joy and friendship, owe their brightness to carotenoids. White roses, symbolizing purity, lack the genetic ability to produce colored anthocyanins or carotenoids in the petals, appearing white due to light reflection.
Complex and Achieved Shades
The colors beyond the primary four are achieved through a careful balance of the existing pigment pathways. Orange, including peach and apricot tones, is an example of this natural blending. It results from the co-accumulation of both red-producing anthocyanins and yellow-producing carotenoids.
The softer, muted shades of peach and apricot are a result of lower concentrations of anthocyanins mixed with the yellow carotenoids. Lavender and mauve roses are the closest the species comes to blue or purple. These colors arise from chemically modified anthocyanins, which shift the red hue toward the violet end of the spectrum.
Bi-color roses display two distinct colors or shades on the same petal due to variations in gene expression controlling pigment distribution. The resulting patterns can manifest as a contrasting edge, a distinct stripe, or a color change from the base to the tip of the petal.
The Missing Colors and Breeding Limits
Despite the vast color range achieved through hybridization, three colors—true blue, true black, and true vibrant green—do not naturally exist in the rose. The primary reason for this is a genetic limitation: the rose genome lacks the gene for the enzyme flavonoid 3′,5′-hydroxylase (F3’5’H). This enzyme is necessary for the production of delphinidin, the specific anthocyanin pigment responsible for true blue and violet hues in flowers like pansies and delphiniums.
Without this enzyme, no amount of traditional cross-breeding can produce a true blue rose. Commercially available “blue” roses are typically deep mauve or lavender, or they are genetically modified. The famous ‘Applause’ rose, for example, was created by inserting the F3’5’H gene from a pansy into a rose, but the result is a high-delphinidin rose that appears mauve-lilac.
Similarly, “black” roses are not truly black but are intensely deep shades of red or burgundy, created by maximizing the concentration of red anthocyanins. True green roses, beyond the green of the sepal, are also non-existent, though some varieties have been bred to display a pale, chartreuse-like hue.