What does 216 color web-safe palette mean?
When in 256 bit color mode [8 bit color depth], browsers have a so-called ‘web-safe’ or ‘browser-safe’ color palette, which is a common denominator for the different computer systems. This palette consists of 256 colors, of which only the first 216 colors are common in the different applications. From the remaining colors, 20 colors are used for the system palette with the last 20 colors being more or less freely available.
