A rose is a rose, or so they say. But a red rose isn't always a red rose. Did you know that a number of factors influence a flower's color? Here are some reasons colors vary in the blooms of a flowering plant:
The pH (measure of acidity/alkalinity) of a soil may influence a plant's bloom color. Hydrangeas (Hydrangea macrophylla) are best known for this. In acidic soils, the blooms show shades of blue. In alkaline soils, the blooms show shades of pink. While soil pH influences a bloom's color, it cannot change it entirely. For example, even in the most alkaline of soils, a blue-flowering cultivar such as ‘Nikko Blue' will never be a clear pink, but instead a muddy blue.
Many flowers fade as they age. For example, a shrub called yesterday, today, and tomorrow (Brunfelsia australis) has purple blooms on the first day. On the second day, they fade to lavender. And on the third day, they're nearly white. Other plants, such as cultivars of lungworts (Pulmonaria spp.), start blue and fade to pink as they age.
Heat can affect the color of blooms. Many tropicals, including passionflowers (Passiflora spp.), display blooms with brighter color in warmer temperatures and duller color in cooler temperatures. On the other hand, many temperate plants work the other way: Cool temperatures enhance their colors and hot temperatures fade them. This is the case for several types of bellflower (Campanula spp.), for example.
Just as a fabric color may look different under store lighting than it does in your home, bloom color may change slightly, depending on lighting conditions. For example, a cool-white bulb will intensify blue, yellow, and orange hues and make reds dull. So, the blooms of a blue-flowering African violet will appear more intense under a cool-white bulb than in natural light. Warm-white bulbs, on the other hand, enhance yellow and orange hues, but fade blue, green, and red. Again, as with fabric, the sun can bleach blooms of some flowers, especially many roses.
When tulips were all the rage in Holland centuries ago, those with broken-colored blooms were the most highly sought after. The blooms displayed more than one color because the bulbs were infected with a virus. Like tulips, other virus-infected plants may have mottled blooms.
The way genetic factors such as color are passed from parent to offspring is complicated. That's why not all the seeds from any one batch will be identical. Sometimes the bloom color may be subtly different, such as a rosy-pink impatiens among a predominantly magenta-pink batch. Other times the bloom color may be markedly different. For example, you might find a white-blooming lobelia among the blue flowers produced from the same packet of seeds.
Sometimes a branch of a plant can change bloom colors spontaneously (or so it seems). This is caused by a variation in a plant gene. If you propagate the branch and grow it into a new plant, the plant is called a sport. Sports are uncommon, but when they occur, they often result in new cultivars. For example, yellow rose ‘Isabella Sprunt' is a sport of apricot rose ‘Safrano'.
It's frustrating to fall in love with a bloom color based on a printed photograph. The growing conditions and lighting are different than yours for the photographed plant. Also, catalogs, books, and magazines may use computer techniques to enhance bloom colors. Ever see a photo of a pure-blue rose in a catalog? You'll seldom see that shade in nature. Color tones vary under certain printing processes, as well.
Florists have techniques to influence bloom color, too. Floral dye is one of them. If you've seen blue or green carnations, chances are they're white carnations that have been put in water laced with blue or green dye. As the flowers absorb the water, they also absorb the coloration.