Colors can be described in many different ways, each method based on a color model. For example, the RGB color model is based on creating colors by adding together varying amounts of red, green, and blue light.
Microsoft Expression Design lets you specify colors by using any one of five different color models: RGB, HSL, HSB, CMYK, and Hex. You can select a color model with the Choose Color Picker drop-down list (at the bottom of the Color Picker). For more information, see Color Picker.
The following is background information about each of these color models:
RGB RGB is an additive color model, which means that the more red, green, and blue you add, the closer the color becomes to white. When you mix an equal amount of red, green, and blue, you always get a neutral gray. To make a color darker, remove equal amounts of all three colors. Computer scanners and monitors are based on the RGB color model, so it is a natural model for describing color on a computer, especially when you work with scanned images. The value for each "channel" (red, green, or blue) can range from 0 (no color) to 255 (fully saturated color). RGB color is also sometimes named 24-bit color or millions of colors.
HLS Many people find the HLS color model more intuitive because it defines colors based on hue, lightness (or brightness), and saturation. To specify a color, you can pick its hue on a rainbow spectrum, select its saturation (the purity of the color), and set its brightness (light to dark). Bright red is a highly saturated, bright color. Pastels such as soft pink are less saturated. You specify hue by a degree (0 to 360 degrees), and specify saturation and lightness with percentages from 0 to 100 percent. Any HLS color with zero saturation is a neutral gray.
HSB The HSB color model is very similar to HLS, except that the B (brightness) value of the color is used instead of lightness.
CMYK The printing done by each printer and printing press is based on three primary colors: cyan, magenta, and yellow. These are named subtractive colors because as you add color you get closer to black. Unfortunately, because inks in the real world are never perfect, you have to add black (K) to achieve a more full range of printed colors. The CMYK model is appropriate primarily when you create images that will be printed. Note that many different combinations of cyan, magenta, yellow, and black define the same color. Defining a neutral gray in CMYK can be tricky (for example, you almost always need more cyan than the other colors), and will change depending on the output device.
You can specify a color based on its hexadecimal values by clicking the Hex field in the lower-right corner of the Color Picker. Hexadecimal numbers are often used when you define web page colors, and always begin with a number sign (#).