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.Send submissions to the contact information listed in thePreface of this book.Color on the Web 29Web Design in a Nutshell, eMatter EditionCopyright © 2000 O Reilly & Associates, Inc.All rights reserved. Color on the WebFor system-level operations, computers use a specific set of 256 colors called thesystem palette.Macs and PCs use a slightly different set of 256 colors in theirsystem palettes.But specific applications may specify a different palette; forinstance, browsers use their own palette, which is substantially different than theWindows system palette (although it s quite similar to the Mac system palette.)Although all colors on computer monitors are made up of combinations of red,green, and blue light, there are actually a number of numerical systems for identi-fying colors, including RGB (red, green, and blue values), Lab (lightness, achannel and b channel), and HSB (hue, saturation, brightness).For purposes of web design, colors are referred to by their numerical RGB values,on a scale from 0 to 255.For instance, the RGB values for a particular dark orangecolor are R:198, G:83, B:52.GammaGamma refers to the overall brightness of a computer monitor s display.In moretechnical terms, it is a numerical adjustment for the nonlinear relationship ofvoltage to light intensity but feel free to think of it as brightness.The defaultgamma setting varies from platform to platform.Images created on a Macintoshwill generally look a lot darker when viewed on a PC or Unix terminal.Imagescreated on a PC will generally look washed out when seen on a Mac.The higherthe gamma value, the darker the display.Table 3-1 shows the standard gammasettings for the major platforms.Table 3-1: Common Default Gamma SettingsPlatform GammaMacintosh 1.8PC 2.5Unix 2.3-2.5One strategy for designing graphics that look acceptable on all platforms is to cali-brate your own monitor to a gamma setting of 2.2, a value that is betweenMacintosh s 1.8 and the PC s 2.5.Bear in mind that your images will look a bitlighter on most Macs and a bit darker on most PCs and Unix terminals than theyappear on your screen, but the jump won t be as drastic as going from one plat-form to another.Color in Browsers (The Web Palette)An interesting problem arises when colors from the full 24-bit color space need tobe displayed on an 8-bit display.Rather than relying on the computer s systempalette, browsers reduce and remap colors to their own built-in palette.This is agreat benefit to web designers because it guarantees that images will look more orless the same on all 8-bit systems.If images were mapped to the various systempalettes, they would look quite different on different platforms.(Note that if thebrowser is running on a 24-bit display, the palette does not come into effect andall colors will be displayed accurately.)30 Chapter 3 Web Design Principles for Print DesignersWeb Design in a Nutshell, eMatter EditionCopyright © 2000 O Reilly & Associates, Inc.All rights reserved. Color on the WebThis Web Palette consists of the 216 colors shared by the Macintosh and PC systempalettes; therefore colors chosen from the Web Palette will render accurately onMac or PC displays.The Web Palette was optimized for Macs and PCs; Unixmachines use a different color model for their system palette, therefore web-safe colors may shift or dither when viewed on Unix terminals.The Web Palette is also known as the Netscape Palette, Netscape 216, Browser-Safe Palette, Web-Safe Palette, Non-dithering Palette, and the 6×6×6 cube.TheWeb Palette is displayed on the web pages for this book at http://www.oreilly.com/catalog/wdnut/.The Web Palette in numbersAn important way to look at the Web Palette is by its numerical values.The WebPalette recognizes six shades of red, six shades of green, and six shades of blue,resulting in 216 possible color values (6×6×6 = 216).This is sometimes referred toas the 6×6×6 color cube.Figure 3-1 shows the cubic nature of this palette
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