We introduce the color wheel for several purposes. One is simply to define the colors of the rose. A second is to describe a model of how roses gain their color. A third is to show how the ordered relationships between colors can help in garden design.
A Color Model
There are yellow, white, and red roses. And in a way, all roses are one of these. Sometimes they are more than one. A copper colored rose, for instance, might contain yellow and magenta pigments. A coral rose might also. Or it might contain only red pigments.
How many pigments the rose might actually have at its disposal is not a question I am prepared to answer. The number is almost certainly larger than three. Still, it is informative to imagine for a moment that the rose is capable of producing just two color pigments:
Those who are familiar with printing know that the classic way to produce red is to mix magenta and yellow pigments in just the right proportions. If the rose practiced this printer's trick, it could produce yellow, red, and purple. Add to this idea that the amount of pigment will govern the darkness, richness, or saturation of the color; and that in the absence of any pigment the rose is white. This set of circumstances will allow a rose to produce every color in the rose spectrum by simply varying the amounts of two pigments it produces.
This model explains why it is that so many reddish roses 'blue.' the yellow pigment that transforms the magenta or purple tones to coral or red fades or bleaches in the sun more quickly than the magenta pigment. The result is that the rose looks more purple or blue.
The fact that most interesting colors in roses, particularly the warmer ones, might be the result of two pigments explains to a great degree why describing and predicting the color of a rose blossom is so fraught with difficulty. Some rose cultivars are highly variable in their production of one or both pigments depending on weather, sunlight, moisture, and soil conditions. Frequently one pigment is less stable than another.
The situation becomes just a little more complex when we consider that there is at least one more color pigment that is something close to pure red. In some roses production of this red pigment depends on sunlight and warmth to develop. This is a red pigment found in such roses as Double Delight, Gemini, Paradise, Mon Cheri, and many others.
Alternatively, roses with this pigment might start yellow, move through orange and pink, and end up red. Mutabilis is the most obvious example. Masquerade and Rainbow's end are other examples.
Using the Color Wheel
One might use this color wheel to design gardens. Notice, for instance, that buff, shell pink, salmon, copper, and vermilion lie on approximately a straight line next to each other. These colors mix and match quite well together. Similarly, pink, rose, cerise, and purple lie on a line. They mix and match quite well.
By comparison, rose doesn't go very well with gold. Mauve can look terrible with yellow. That said, most roses have soft enough colors that they will consort happily with most other roses.
One does want to be a little careful with the saturated gold, orange, vermilion, scarlet, and red. These work well together, but can look out of place mixed higgelty piggelty with pastel colors. One might also try candy pink, salmon, coral, pale apricot, and apricot together.
The general rule is that colors that have obvious relationships to each other on the color wheel will frequently work well together. When it is difficult to explain the spacial relationships between the colors on the wheel, it is frequently true that the colors will not work well together.
There are several major distinctions that are helpful. One is the distinction between warm and cool colors. Draw a line from white to red. The colors that lie above this line are warm colors. Those that lie below the line are cool colors. As a general rule, warm colors consort best with warm colors and cool colors consort best with cool colors.
A second distinction is between saturated colors and unsaturated colors, sometimes referred to as pastels. Saturated colors are the ones around the outside rim of the wheel. Pastels are ones that approach white. Saturated colors pack a color whallop, and may clash violently. Pastels tend to blend better, allowing for a little more recklessness.
Some of the most distictive and striking designs arise from stretching the rules close to the breaking point. One can, for example, combine pink and yellow effectively: one simply has to be sure that the saturation of each is about the same.
Roses produce a wide variety of garden-friendly blossoms. Any gardener who plans and plants carefully, works diligently, and fearlessly tears up garden plantings that just don't work is bound to end up with a striking and glorious place full of harmonious color. Make your best guesses, plant your favorite roses, and enjoy the garden.