TS-688

Defining Colors using Hex Values

With the Gray-Scale and RGB Color Naming Schemes

Introduction

In Version 6, SAS/Graph includes predefined names for 290 different colors. Additional predefined color names became available for over 100 colors for SAS/Graph output in Version 9. These are the HTML color names listed in the SAS Registry. Together the list of predefined colors give you over 400 colors to choose from. See the "Predefined Colornames" section of this document for the names of the available pre-defined colors.

In any of these releases of the SAS system, you can also define your own colors in SAS/Graph using one of the color-naming schemes. The color-naming schemes are documented in the "SAS/Graph Software Reference" section of the OnlineDoc, under "SAS/Graph Colors". This document focuses on two of those schemes, gray-scale and RGB.

Using the gray-scale color-naming system, it is possible to define 256 different shades of gray ranging from pure black to pure white. With the RGB color-naming system, it is possible to define over 16 million colors. Both color-naming schemes in SAS use hexadecimal notation to define the colors.

Understanding Hex Values

In everyday life we typically use numbers from the base 10 system, where values range from 0 to 9 before an additional digit is needed. In a hexadecimal numbering system, each digit can represent 16 values, typically represented as 0 through 9 and then A through F, as shown in the following table.

In the base 10 system, a two-digit number can represent 100 values ranging from 0 through 99. In the base 16 system, a two digit number can represent 256 values, ranging from 00 through FF. A six-digit number in the base 10 system represents 10⁶ (10 x 10 x 10 x 10 x 10 x 10) values, or 1,000,000 numbers. A six-digit number in the hexadecimal system represents 16⁶ (16 x 16 x 16 x 16 x 16 x 16) values, or 16,777,215 numbers.

Methods for manipulating numbers, such as addition, subtraction, and multiplication, work the same in both systems; it is the representation of the value that is different. For example, each of these equations represents the same values:

When using the hexadecimal system to define you own colors, the exact value for the color is not as significant as the relationship of the digits in the value to each other, and the relationship of the value of this color to other colors.

The Gray-Scale Color-Naming Scheme

The gray-scale color naming scheme uses a two digit hex value to define up to 256 shades of gray. In SAS, the root word GRAY is used to distinguish this naming system from the other color-naming systems. For example, GRAY00 is black, GRAYFF is white, and GRAY88 is a medium gray.

The following chart displays all 256 Gray-scale colors.

Gray-Scale Colors

To define the Gray-scale colors using this chart, build the names as follows:

For example, the last square on the bottom right represents the value GRAY0F, a very dark gray. The square on the top of the left vertical axis represents the value GRAYF0, a very light gray.

The RGB Color-Naming System

The RGB color system is commonly used in both web graphics and web documents. This system is was designed to define colors as the human eye perceives them, as light. The three foundation or primary colors of this system are red, green, and blue.

The color system is additive: varying values for red, green, and blue can be combined to form the other colors. Because the system is based upon the properties of light, an absence of all color is black and full saturation in all colors is white. Each secondary color is the sum of two primary colors:

• Red + Blue = Purple
• Red + Green = Yellow
• Green + Blue = Cyan

The SAS RGB color-naming scheme is similar to the standard HTML color-naming scheme. Both use a six-digit hexadecimal value to represent the amount of red, green, and blue that define the color. The first pair of digits represents the amount of red in the color; the second pair of digits is for blue, and the third is for green. In SAS, the color names must also be preceded by the letters "CX" to distinguish this color-naming system from other SAS color-naming systems. The general form of the names in SAS is as follows:

This system allows for the creation of over 16 million different colors. All 256 grayscale colors are included in this color system.

Listing the RGB Colors

Because the RGB system defines over 16 million colors, it would take many pages to display them all. It is also difficult to distinguish colors that have very similar values.

A good reference for a broad range of colors are the 216 colors commonly used on the web. These 216 colors form what is known as the "web-safe" or "non-dithering" color palette. They were traditionally used to prevent color-mapping or dithering of images when the majority of computer displays only supported 256 colors. Although most displays today are capable of representing millions of colors, this palette still remains popular.

The only digits used in web-safe colors are 0, 3, 6, 9, C, and F. As you can see in the chart, the convention is for the values of red, green, and blue to use the same value for both digits.

The 216-Websafe Colors

By varying the amounts of red, green, and blue in a given value, you can begin to define your own colors. Remember that the names must be preceded by the letters "CX" in order to identify the value as an RGB color in SAS.

Converting Color Values from Other Software Programs

Many software programs that allow you to edit their own colors can display the RGB values for that color. In these programs the RGB colors are usually represented as three base-10 values ranging from 0 to 255. For example, the following screen-shots show the RGB values for a particular shade of blue as displayed by two different software programs:

To match RGB colors in your SAS output to RGB colors from another software program, you can translate the decimal values to hexadecimal representation using a SAS program. For example, the following program converts the color blue above from the base 10 representation to hexadecimal values that can be used to represent the RGB color in SAS.

	data _null_;

	/* Input values */

	�red=42;

	�green=31;

	�blue=170;

	
	/* Convert to hex */

	�hexred=put(red,hex2.);

	�hexgreen=put(green,hex2.);

	�hexblue=put(blue,hex2.);

	
	/* Create as a SAS RGB color */

	�sasrgb="CX"||hexred||hexgreen||hexblue;

	
	/* Write the new value to the Log */

	�put sasrgb;

	run;

For this shade of blue, the SAS RGB color is CX2A1FAA.

Predefined Colornames

In SAS 6, 290 different colors were available by their predefined names, such as RED, ORANGE, and VIGB ("vivid greenish blue"). In SAS 8.2, 140 predefined colors were added that could be used with non-graphical output. In Version 9.0, you can specify these HTML colors for SAS/Graph output. These colors, such as BlanchedAlmond and SeaShell, are listed in the SAS Registry under the key "COLORNAMES\HTML". The RGB values for the colors are displayed next to each name.

The following table shows the SAS/Graph color names and the HTML color names. The presence of a Description indicates the color is one of the SAS/Graph colors. RGB and HLS colors are shown for both types of colors. The color should be referenced by its name, RGB, or HLS value. Names do not contain spaces, so they do not need to be specified in quotes. Colors listed by both schemes, such as BLACK and YELLOW, are represented only once in the table.