The Safety Palette
The safety palette is a set of 216 different colors that are designed to be rendered in their original form by browsers running on the Windows and Macintosh operating systems.
The safety palette is important to ensure accurate color representation in a Web page. Colors that cannot be rendered by a browser are dithered, in which alternating pixels of similar colors are used, approximating the original color's appearance. Dithering can cause images to appear with jagged edges and fuzzy colors. The advantage of the safety palette, is that its colors will not require dithering. To understand why, we must first review how colors are defined by HTML.
A specific color is identified by the mixture of the three primary colors: red, green, and blue. The intensity of the color is indicated by a numeric value: 0 for the lowest intensity up to 255 - the highest intensity. A specific color value is indicated by a triplet of the red, green, and blue values. For example, the color black has the color triplet: (0, 0, 0). The color white is represented by the color triplet: (255, 255, 255). Yellow, which is an equal mixture of red and green, is equal to the color value: (255, 255, 0). The total number of unique colors that can be represented by this system is 2553, or 16,581,375. This is more colors than the human eye can distinguish.
In HTML, these color triplets are represented in hexadecimal values. Hexadecimals are numbers from a base-16, rather than base-10, counting system. The numbers 0 through 16 in base-16 are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F. The number 17 is represented as 10. Under this system, the color white appears as #FFFFFF, since FF is the base-16 representation of the number 255. The color yellow would be: #FFFF00.
Now let's return to the safety palette. The red, green, and blue colors of the safety palette must be equal to one of the following six hexadecimal numbers: 00, 33, 66, 99, CC, or FF. Thus, a color value of #33FF66 would found in the safety palette, but a color value of #33AA44, would not. Since each color has six possible values, there are 6x6x6 or 216 total colors in the safety palette.
This page shows all of the colors of the safety palette along with their hexadecimal color values. Note that the safety palette is only important for monitors that limit their color resolution to 256 colors. A monitor that has a higher color resolution will not have to employ dithering. With monitors now regularly displaying colors under higher resolutions, the importance of the safety palette is not as great as it once was.