Lilacs (Syringa) are among the most beloved spring-blooming shrubs. The perceived color of these flowers often leads to confusion, as shades can appear drastically different depending on the light and the viewer’s interpretation. To bring clarity to the true spectrum of these plants, a formal system is necessary to categorize the vast array of hues. This classification helps growers, breeders, and gardeners accurately define the color of a specific cultivar against a common standard.
The Standardized Lilac Color Classification
The precise number of recognized lilac colors is governed by a formal system established by the International Lilac Society (ILS). This organization manages the official registry for all Syringa cultivars. The ILS standard divides the entire visible color range of lilacs into seven distinct color classes. The official categories include White, Violet, Blue, Lilac (the color itself), Pink, Magenta, and Purple. This standardized system allows for the accurate documentation of new cultivars, ensuring that a lilac registered as “Blue” in one country is recognized under the same class elsewhere.
Exploring the Major Color Categories
The Blue classification (Class III) rarely presents as a true sky blue; instead, these cultivars exhibit tones closer to a deep lavender or periwinkle. The French hybrid ‘President Lincoln’ is a classic example, known for its fragrant, single flowers that register as a clear, medium-toned blue within this spectrum.
The Magenta category (Class VI) is a vibrant and distinct group, covering reddish-purple shades that are often mistaken for deep pink or red. Cultivars like ‘Congo’ display the rich, warm, reddish tones that define this class. The famous ‘Sensation’ cultivar is a unique example, classified by its primary color but notable for its distinct white picotee edge on each magenta floret.
The official Lilac class (Class IV) is reserved for the medium, pale purple color that gave the flower its name, acting as the midpoint between violet and pink. The Purple class (Class VII) encompasses the deepest, richest, reddish-purple hues, often appearing the darkest of all non-white flowers. Meanwhile, the White (Class I) and Pink (Class V) classes cover pure white blossoms and flowers with a clear, soft pink hue, respectively.
Factors That Influence Lilac Color Appearance
The color of a lilac blossom, while genetically fixed to its registered class, can appear to shift significantly due to environmental and temporal factors. The degradation of the anthocyanin pigments responsible for the purple, pink, and magenta hues is the most common cause. Intense heat, especially during the early stages of bud development or flowering, can break down these pigments, causing the flowers to open with a bleached or washed-out appearance.
The intensity of sunlight directly affects the saturation and depth of the color that develops in the petal cells. Lilacs grown in full sun generally produce blossoms with more intense, deep colors because UV light can stimulate the plant to produce more protective anthocyanin compounds. In contrast, a lilac that receives too much shade may have flowers that appear paler or less vibrant than expected.
The age of the bloom also contributes to its color appearance, as the hue often changes subtly from the moment the bud first opens. Many deeply colored cultivars will start as a dark, intense shade and gradually fade or lighten to a softer tone as the individual florets mature.