Web-safe, or Browser-safe palettes as they are also referred to, consist of 216 colors that display solid, non-dithered, and consistent* on any computer monitor, or Web browser, capable of displaying at least 8-bit color (256 colors). The reason why this palette contains only 216 colors, instead of the maximum 256 colors, is that only 216 out of the basic 256 colors will display exactly the same on all computers.
In the olden days, (ten or so years ago), most computers were only capable of displaying a maximum of 256 colors at one time. There were many reasons for these color limitations, the high cost of video RAM being the foremost. Most early video/graphics cards had between 128 and 512K of video RAM, or enough to display 16 to 256 colors. To display more colors, more RAM is needed.
This compares to computers over the past five years that ship with monitors capable of displaying 24-bit (or 32-bit) color, which equates to a possible 16.7 million colors. So it is only to meet the needs of the lowest common denominator, those color-challenged dinosaurs, that we are forced to limit ourselves to a palette of only 216 colors when we have the built-in capabilities to see millions.
Admittedly, some of these relics may remain in use. But are they more than color deficient? They are not even capable of properly displaying the majority of today's sophisticated Web sites that are loaded with animation, images and even video. What kind of Internet connection do they have to reasonably display the data? Can they handle the basic day-to-day use of graphic extensive applications and games which also utilize more than just 256 colors? To accommodate such needs, older computers would have needed to be upgraded. And who would have upgraded their computer without upgrading its color display capacity?
OK, you are still concerned, but you decide to experiment. You create a page or JPEG graphic using some PANTONE Colors you've been dying to use for years. The results look great for those computer savvy in your market. Now test it for the 256-limited. Simply turn the color setting of your monitor to 256 colors and its lowest screen resolution, then analyze the impact. Maybe things aren't as bad as you thought.
The need for using Web-safe only colors is predicated on the assumption that enough of your intended audience is still using color displays that can only view 256 colors. Year by year, such displays are fading from existence. Further, with Internet communication speed faster than ever due to the wide-spread use of cable modems and T1 lines, the limiting of color content for faster download is also diminished.
So the questions to ask yourself are: How many people in my target audience are actively using antiquated equipment and is the number worth depriving the majority the color they deserve?
*Even with Web-safe colors, total consistency from monitor to monitor is not attainable due to manufacturing differences, aging, user controlled settings, ambient lighting conditions and each individual's perception of color.
Portions reprinted with permission from Gary W. Priester: from his article All You Need to Know About Web Safe Colors.