ArcGIS Blog

Colors in ArcGIS symbols

By Aileen Buckley, Mapping Center Lead, and Jeremy Wright, John Cranfill, and Michael Grossman, Product Engineers

Colors in ArcGIS Symbols - Thumbnail

There are three primary building blocks of standard symbols in ArcGIS—fonts, colors, and graphic files. In a previous article, we discussed fonts in ArcGIS symbols, and in an upcoming article we will tackle the issue of pictures. In this article, we discuss colors in ArcGIS symbols, including color models and how they are used to define colors in ArcGIS, and the differences between their color gamuts. We wrap up with a set of tips for working with color in ArcGIS.

Color models

The first thing to understand about colors in ArcGIS symbols is that they are defined using a color model, which is a system for specifying colors numerically according to their individual components. A color model is visualized as a three-dimensional space that contains all possible combinations of the model’s primary colors.

The RGB color model

An RGB color space is created by mapping its primary colors—red, green, and blue (RGB)—into a 3-D Cartesian coordinate system. This results in a 3-D cube like the one shown in figure 1.

Colors in ArcGIS Symbols - Figure 1

Figure 1. The RGB color model

With its primary colors at three corners, the secondary colors—cyan, magenta, and yellow (CMY)—in addition to black and white, are assigned to the remaining corners.

The values for RGB range from 0 to 255 for each dimension, yielding 2563 (16,777,216) possible colors. In this color model, black is defined as (0,0,0) and white as (255,255,255). Gray is scaled along the diagonal line between the two opposing corners between black and white.

RGB is an additive color model because it describes what kind of light needs to be mixed together (emitted) to create the various colors. In this color model, the combination of all colors is white (figure 2).

Colors in ArcGIS Symbols - Figure 2

Figure 2. The primary colors of the RGB color model are red, green, and blue, and the combination of all colors is white (from AM Tait’s Ten quick references for map makers)

This model is used for electronic devices that emit light of different colors, such as smart phones, computers, and televisions.

The CMY and CMYK color models

The CMY color space is based on a subtractive color model which describes what kind of inks need to be mixed together so light reflected from the surface and through the inks produces the various colors.

A CMY color space can also be visualized as a cube with its primary colors (cyan, yellow, and magenta) at three corners, and its secondary colors (red, green, and blue) along with black and white, at the other corners (figure 3).

Colors in ArcGIS Symbols - Figure 3

Figure 3. The CMY color model

Values for the primary colors of this color model are expressed in percentages and range from 0 to 100. In this color model, the combination of all colors is black (figure 4).

Colors in ArcGIS Symbols - Figure 4

Figure 4. The primary colors of the CMY color model are cyan, magenta, and yellow, and the combination of all colors is black (from AM Tait’s Ten quick references for map makers)

The CMYK color space, a variation on the CMY model, adds black. This color model is used in color printing, and its name reflects the four common components of ink formulas used by some printers and plotters.

The HSV color model

Another color model that ArcGIS supports is HSV (hue, saturation, and value), which can be visualized as a cone in a cylindrical coordinate system (figure 5). HSV is actually just a rearrangement of the geometry of the RGB color model in an attempt to be more intuitive and perceptually relevant than the Cartesian (cube) representation.

Colors in ArcGIS Symbols - Figure 5

Figure 5. The HSV color model

In this color model, the primary and secondary colors are arranged around the circle that represents the top of the cone, so that the hue dimension of color (what we commonly think of as “color”, such as red, orange, or yellow) can be expressed as angles varying counterclockwise from red at zero. The saturation dimension of color, which is the extent to which it departs from a neutral color such as gray, or in simpler terms, its “colorfulness”, ranges from 0 percent (gray) at the middle to 100 at the face, or curved surface of the cone’s exterior, where the colors are fully saturated. The value dimension of color, or the intensity of white in the color, ranges from zero percent (black) at the tip of the cone to 100 percent at the top. Gray tones fall along this vertical axis.

Defining colors in ArcMap

In ArcMap, you will use one of these models to define colors in the Color Selector dialog box. You can switch between color models by selecting a different model from the drop-down menu (figure 6).

Colors in ArcGIS Symbols - Figure 6

Figure 6. Changing colors models in the Color Selector dialog box

You can use the Advanced Selection option to modify the colors using a graphic representation of the color space (figure 7).

Colors in ArcGIS Symbols - Figure 7

Figure 7. You can also modify colors using a graphic representation of the color space

Recommendations for defining colors in ArcGIS

You should consider defining colors in a way that matches your intended display mode. Use RGB to define colors for a map that will be primarily viewed on-screen: shared on ArcGIS.com or via an ArcGIS Server instance, or viewed in a PDF on a mobile device. Use CMYK to define colors for a map intended for printing or that will be sent to a service bureau for reproduction.

The HSV color model is good to use when you want to change one component of color. In many cases, this is the easier way to modify a color because it is simpler to understand than trying to change the red, green, blue, cyan, magenta, yellow, or black components of color. Then, once you have defined a color using the HSV color model, you can convert it to RGB or CMYK, depending on how your map will be viewed.

Although you can easily switch between color models, you should be aware that you may not always see exactly the same color if you switch between RGB/HSV and CMYK. The reason is that these two color spaces don’t have equivalent “gamuts”.

Color gamuts

Although any color model can theoretically be used to create any color, each color model has its own gamut. A color gamut is a certain complete subset of colors that can be accurately represented in a given circumstance, such as with a certain color model and/or output device.

These RGB/HSV and CMYK color models are just ways of numerically representing actual light—either transmitted or reflected to your eye. They both can describe a subset of the visible spectrum, but they can’t reproduce the same subset of the visible spectrum. Figure 8 is a visualization of variations in the gamuts of selected color models.

Colors in ArcGIS Symbols - Figure 8

Figure 8. The print gamuts in the visible color spectrum for select color models (from http://www.printernational.org/rgb-versus-cmyk.php)

RGB and CMYK models are “device dependent” color models. This means that, as numeric representations of real colors, they will be interpreted by the devices they are displayed or printed on. This interpretation varies from device to device, so the same RGB numbers can yield very different color appearances when viewed on two different monitors, for example.

The capabilities of display devices will affect the color gamut as well. For RGB, a monitor with a better backlight and LCD panel may have a broader gamut than a cheaper consumer grade one. That’s why people pay for fancier monitors when they’re doing graphic design all day than if they’re just surfing the web occasionally.

In general, it can be said that the CMYK color model has a smaller gamut than the RGB color model, and that printing devices have a more restricted color gamut than does a television, which is more restricted than an LCD screen, which is more restricted than photographic film, which is more restricted than laser video projectors. In printing, the color gamut in printing is affected by many factors, including the ink formulation, printing process, substrate, and halftoning or lay down technique.

Tips for working with color in ArcGIS

To learn more

Here are some online help topics that will allow you to learn more about color in ArcGIS symbols:

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